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 $24.29   4.372%   $25.352   $25.35   $25.35   $25.40  
  Purchase #2 $173.48   11.582%   $193.5725   $193.57   $193.55   $193.60  
  Purchase #3 $68.60   5.299%   $72.2351   $72.24   $72.25   $72.20  
  Purchase #4 $134.29   3.481%   $138.9646   $138.96   $138.95   $139.00  
  Purchase #5 $197.29   10.630%   $218.2619   $218.26   $218.25   $218.30  
  Purchase #6 $59.89   6.544%   $63.8092   $63.81   $63.80   $63.80  
  Purchase #7 $150.51   4.403%   $157.137   $157.14   $157.15   $157.10  
  7 purchase totals = $808.35       $869.3323   $869.33   $869.30   $869.40