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 $245.90   5.849%   $260.2827   $260.28   $260.30   $260.30  
  Purchase #2 $174.38   13.756%   $198.3677   $198.37   $198.35   $198.40  
  Purchase #3 $89.68   13.340%   $101.6433   $101.64   $101.65   $101.60  
  Purchase #4 $110.67   5.431%   $116.6805   $116.68   $116.70   $116.70  
  Purchase #5 $180.60   7.686%   $194.4809   $194.48   $194.50   $194.50  
  Purchase #6 $233.87   7.276%   $250.8864   $250.89   $250.90   $250.90  
  Purchase #7 $118.90   4.781%   $124.5846   $124.58   $124.60   $124.60  
  7 purchase totals = $1,154.00       $1,246.9261   $1,246.92   $1,247.00   $1,247.00