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 $118.49   11.409%   $132.0085   $132.01   $132.00   $132.00  
  Purchase #2 $224.80   13.500%   $255.148   $255.15   $255.15   $255.10  
  Purchase #3 $157.96   11.176%   $175.6136   $175.61   $175.60   $175.60  
  Purchase #4 $188.30   6.788%   $201.0818   $201.08   $201.10   $201.10  
  Purchase #5 $234.92   5.548%   $247.9534   $247.95   $247.95   $248.00  
  Purchase #6 $113.38   5.749%   $119.8982   $119.90   $119.90   $119.90  
  Purchase #7 $53.94   4.103%   $56.1532   $56.15   $56.15   $56.20  
  7 purchase totals = $1,091.79       $1,187.8567   $1,187.85   $1,187.85   $1,187.90