Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $129.91   12.391%   $146.0071   $146.01   $146.00   $146.00  
  Purchase #2 $201.49   7.363%   $216.3257   $216.33   $216.35   $216.30  
  Purchase #3 $123.65   13.483%   $140.3217   $140.32   $140.30   $140.30  
  Purchase #4 $165.28   13.280%   $187.2292   $187.23   $187.25   $187.20  
  Purchase #5 $96.73   13.344%   $109.6377   $109.64   $109.65   $109.60  
  Purchase #6 $195.56   5.850%   $207.0003   $207.00   $207.00   $207.00  
  Purchase #7 $205.33   3.746%   $213.0217   $213.02   $213.00   $213.00  
  7 purchase totals = $1,117.95       $1,219.5434   $1,219.55   $1,219.55   $1,219.40