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 $182.60   13.336%   $206.9515   $206.95   $206.95   $207.00  
  Purchase #2 $24.33   4.825%   $25.5039   $25.50   $25.50   $25.50  
  Purchase #3 $118.94   4.706%   $124.5373   $124.54   $124.55   $124.50  
  Purchase #4 $232.26   9.550%   $254.4408   $254.44   $254.45   $254.40  
  Purchase #5 $66.29   10.602%   $73.3181   $73.32   $73.30   $73.30  
  Purchase #6 $29.44   4.383%   $30.7304   $30.73   $30.75   $30.70  
  Purchase #7 $71.74   8.572%   $77.8896   $77.89   $77.90   $77.90  
  7 purchase totals = $725.60       $793.3716   $793.37   $793.40   $793.30