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 $239.97   12.426%   $269.7887   $269.79   $269.80   $269.80  
  Purchase #2 $136.39   6.584%   $145.3699   $145.37   $145.35   $145.40  
  Purchase #3 $207.54   7.296%   $222.6821   $222.68   $222.70   $222.70  
  Purchase #4 $213.30   3.127%   $219.9699   $219.97   $219.95   $220.00  
  Purchase #5 $234.70   13.165%   $265.5983   $265.60   $265.60   $265.60  
  Purchase #6 $188.75   9.807%   $207.2607   $207.26   $207.25   $207.30  
  Purchase #7 $128.29   12.723%   $144.6123   $144.61   $144.60   $144.60  
  7 purchase totals = $1,348.94       $1,475.2819   $1,475.28   $1,475.25   $1,475.40