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 $245.92   6.346%   $261.5261   $261.53   $261.55   $261.50  
  Purchase #2 $46.52   13.717%   $52.9011   $52.90   $52.90   $52.90  
  Purchase #3 $219.32   8.268%   $237.4534   $237.45   $237.45   $237.50  
  Purchase #4 $148.27   4.505%   $154.9496   $154.95   $154.95   $154.90  
  Purchase #5 $63.66   8.651%   $69.1672   $69.17   $69.15   $69.20  
  Purchase #6 $44.65   8.646%   $48.5104   $48.51   $48.50   $48.50  
  Purchase #7 $189.30   3.168%   $195.297   $195.30   $195.30   $195.30  
  7 purchase totals = $957.64       $1,019.8048   $1,019.81   $1,019.80   $1,019.80