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 $20.48   8.299%   $22.1796   $22.18   $22.20   $22.20  
  Purchase #2 $109.26   12.819%   $123.266   $123.27   $123.25   $123.30  
  Purchase #3 $187.80   13.728%   $213.5812   $213.58   $213.60   $213.60  
  Purchase #4 $137.63   5.362%   $145.0097   $145.01   $145.00   $145.00  
  Purchase #5 $163.69   6.620%   $174.5263   $174.53   $174.55   $174.50  
  Purchase #6 $215.64   6.205%   $229.0205   $229.02   $229.00   $229.00  
  Purchase #7 $212.40   4.262%   $221.4525   $221.45   $221.45   $221.50  
  7 purchase totals = $1,046.90       $1,129.0358   $1,129.04   $1,129.05   $1,129.10