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 $85.44   10.749%   $94.6239   $94.62   $94.60   $94.60  
  Purchase #2 $160.73   3.761%   $166.7751   $166.78   $166.80   $166.80  
  Purchase #3 $90.38   8.349%   $97.9258   $97.93   $97.95   $97.90  
  Purchase #4 $61.96   12.566%   $69.7459   $69.75   $69.75   $69.70  
  Purchase #5 $116.36   5.596%   $122.8715   $122.87   $122.85   $122.90  
  Purchase #6 $136.59   8.187%   $147.7726   $147.77   $147.75   $147.80  
  Purchase #7 $47.58   4.869%   $49.8967   $49.90   $49.90   $49.90  
  7 purchase totals = $699.04       $749.6115   $749.62   $749.60   $749.60