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 $97.78   6.667%   $104.299   $104.30   $104.30   $104.30  
  Purchase #2 $196.47   8.479%   $213.1287   $213.13   $213.15   $213.10  
  Purchase #3 $74.59   9.282%   $81.5134   $81.51   $81.50   $81.50  
  Purchase #4 $250.74   8.650%   $272.429   $272.43   $272.45   $272.40  
  Purchase #5 $23.80   10.244%   $26.2381   $26.24   $26.25   $26.20  
  Purchase #6 $193.27   6.408%   $205.6547   $205.65   $205.65   $205.70  
  Purchase #7 $30.92   4.763%   $32.3927   $32.39   $32.40   $32.40  
  7 purchase totals = $867.57       $935.6556   $935.65   $935.70   $935.60