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 $66.83   4.253%   $69.6723   $69.67   $69.65   $69.70  
  Purchase #2 $123.34   11.340%   $137.3268   $137.33   $137.35   $137.30  
  Purchase #3 $100.66   11.700%   $112.4372   $112.44   $112.45   $112.40  
  Purchase #4 $223.48   4.869%   $234.3612   $234.36   $234.35   $234.40  
  Purchase #5 $169.35   5.553%   $178.754   $178.75   $178.75   $178.80  
  Purchase #6 $223.95   7.316%   $240.3342   $240.33   $240.35   $240.30  
  Purchase #7 $43.54   11.412%   $48.5088   $48.51   $48.50   $48.50  
  7 purchase totals = $951.15       $1,021.3945   $1,021.39   $1,021.40   $1,021.40