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 $151.95   10.162%   $167.3912   $167.39   $167.40   $167.40  
  Purchase #2 $129.31   13.268%   $146.4669   $146.47   $146.45   $146.50  
  Purchase #3 $76.50   12.379%   $85.9699   $85.97   $85.95   $86.00  
  Purchase #4 $88.68   7.541%   $95.3674   $95.37   $95.35   $95.40  
  Purchase #5 $211.43   11.525%   $235.7973   $235.80   $235.80   $235.80  
  Purchase #6 $108.66   3.203%   $112.1404   $112.14   $112.15   $112.10  
  Purchase #7 $154.64   8.323%   $167.5107   $167.51   $167.50   $167.50  
  7 purchase totals = $921.17       $1,010.6438   $1,010.65   $1,010.60   $1,010.70