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 $161.70   13.399%   $183.3662   $183.37   $183.35   $183.40  
  Purchase #2 $247.92   5.276%   $261.0003   $261.00   $261.00   $261.00  
  Purchase #3 $147.35   12.323%   $165.5079   $165.51   $165.50   $165.50  
  Purchase #4 $76.79   3.278%   $79.3072   $79.31   $79.30   $79.30  
  Purchase #5 $173.73   11.779%   $194.1937   $194.19   $194.20   $194.20  
  Purchase #6 $229.35   8.138%   $248.0145   $248.01   $248.00   $248.00  
  Purchase #7 $124.38   11.176%   $138.2807   $138.28   $138.30   $138.30  
  7 purchase totals = $1,161.22       $1,269.6705   $1,269.67   $1,269.65   $1,269.70