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 $247.92   13.464%   $281.2999   $281.30   $281.30   $281.30  
  Purchase #2 $84.72   12.846%   $95.6031   $95.60   $95.60   $95.60  
  Purchase #3 $183.51   5.756%   $194.0728   $194.07   $194.05   $194.10  
  Purchase #4 $91.84   9.610%   $100.6658   $100.67   $100.65   $100.70  
  Purchase #5 $118.87   13.806%   $135.2812   $135.28   $135.30   $135.30  
  Purchase #6 $101.35   12.425%   $113.9427   $113.94   $113.95   $113.90  
  Purchase #7 $102.68   11.356%   $114.3403   $114.34   $114.35   $114.30  
  7 purchase totals = $930.89       $1,035.2058   $1,035.20   $1,035.20   $1,035.20