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 $222.55   11.419%   $247.963   $247.96   $247.95   $248.00  
  Purchase #2 $191.56   7.365%   $205.6684   $205.67   $205.65   $205.70  
  Purchase #3 $59.53   7.643%   $64.0799   $64.08   $64.10   $64.10  
  Purchase #4 $97.51   8.781%   $106.0724   $106.07   $106.05   $106.10  
  Purchase #5 $238.91   3.597%   $247.5036   $247.50   $247.50   $247.50  
  Purchase #6 $244.81   6.683%   $261.1707   $261.17   $261.15   $261.20  
  Purchase #7 $221.74   8.459%   $240.497   $240.50   $240.50   $240.50  
  7 purchase totals = $1,276.61       $1,372.9550   $1,372.95   $1,372.90   $1,373.10