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 $233.96   11.695%   $261.3216   $261.32   $261.30   $261.30  
  Purchase #2 $99.99   13.462%   $113.4507   $113.45   $113.45   $113.50  
  Purchase #3 $181.45   11.106%   $201.6018   $201.60   $201.60   $201.60  
  Purchase #4 $195.28   4.616%   $204.2941   $204.29   $204.30   $204.30  
  Purchase #5 $42.84   13.298%   $48.5369   $48.54   $48.55   $48.50  
  Purchase #6 $44.87   12.441%   $50.4523   $50.45   $50.45   $50.50  
  Purchase #7 $146.40   11.722%   $163.561   $163.56   $163.55   $163.60  
  7 purchase totals = $944.79       $1,043.2184   $1,043.21   $1,043.20   $1,043.30