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 $68.93   11.422%   $76.8032   $76.80   $76.80   $76.80  
  Purchase #2 $249.27   7.215%   $267.2548   $267.25   $267.25   $267.30  
  Purchase #3 $45.75   9.797%   $50.2321   $50.23   $50.25   $50.20  
  Purchase #4 $166.86   8.285%   $180.6844   $180.68   $180.70   $180.70  
  Purchase #5 $40.42   5.222%   $42.5307   $42.53   $42.55   $42.50  
  Purchase #6 $118.48   3.342%   $122.4396   $122.44   $122.45   $122.40  
  Purchase #7 $249.43   9.398%   $272.8714   $272.87   $272.85   $272.90  
  7 purchase totals = $939.14       $1,012.8162   $1,012.80   $1,012.85   $1,012.80