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 $56.79   8.174%   $61.432   $61.43   $61.45   $61.40  
  Purchase #2 $233.35   6.448%   $248.3964   $248.40   $248.40   $248.40  
  Purchase #3 $50.43   11.731%   $56.3459   $56.35   $56.35   $56.30  
  Purchase #4 $57.28   5.190%   $60.2528   $60.25   $60.25   $60.30  
  Purchase #5 $125.95   5.281%   $132.6014   $132.60   $132.60   $132.60  
  Purchase #6 $75.68   12.339%   $85.0182   $85.02   $85.00   $85.00  
  Purchase #7 $119.91   8.121%   $129.6479   $129.65   $129.65   $129.60  
  7 purchase totals = $719.39       $773.6946   $773.70   $773.70   $773.60