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 $54.97   3.457%   $56.8703   $56.87   $56.85   $56.90  
  Purchase #2 $126.34   6.199%   $134.1718   $134.17   $134.15   $134.20  
  Purchase #3 $156.28   8.455%   $169.4935   $169.49   $169.50   $169.50  
  Purchase #4 $104.66   11.453%   $116.6467   $116.65   $116.65   $116.60  
  Purchase #5 $160.91   6.158%   $170.8188   $170.82   $170.80   $170.80  
  Purchase #6 $168.91   11.737%   $188.735   $188.74   $188.75   $188.70  
  Purchase #7 $116.68   7.872%   $125.865   $125.87   $125.85   $125.90  
  7 purchase totals = $888.75       $962.6011   $962.61   $962.55   $962.60