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 $66.54   11.134%   $73.9486   $73.95   $73.95   $73.90  
  Purchase #2 $55.28   7.344%   $59.3398   $59.34   $59.35   $59.30  
  Purchase #3 $226.52   8.315%   $245.3551   $245.36   $245.35   $245.40  
  Purchase #4 $214.25   9.397%   $234.3831   $234.38   $234.40   $234.40  
  Purchase #5 $139.40   7.251%   $149.5079   $149.51   $149.50   $149.50  
  Purchase #6 $116.68   12.485%   $131.2475   $131.25   $131.25   $131.20  
  Purchase #7 $241.57   12.313%   $271.3145   $271.31   $271.30   $271.30  
  7 purchase totals = $1,060.24       $1,165.0965   $1,165.10   $1,165.10   $1,165.00