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 $37.56   11.611%   $41.9211   $41.92   $41.90   $41.90  
  Purchase #2 $141.92   8.803%   $154.4132   $154.41   $154.40   $154.40  
  Purchase #3 $97.98   10.273%   $108.0455   $108.05   $108.05   $108.00  
  Purchase #4 $36.91   10.176%   $40.666   $40.67   $40.65   $40.70  
  Purchase #5 $93.40   4.270%   $97.3882   $97.39   $97.40   $97.40  
  Purchase #6 $58.45   6.195%   $62.071   $62.07   $62.05   $62.10  
  Purchase #7 $181.34   6.861%   $193.7817   $193.78   $193.80   $193.80  
  7 purchase totals = $647.56       $698.2867   $698.29   $698.25   $698.30