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 $232.57   12.503%   $261.6482   $261.65   $261.65   $261.60  
  Purchase #2 $70.42   7.200%   $75.4902   $75.49   $75.50   $75.50  
  Purchase #3 $164.63   7.591%   $177.1271   $177.13   $177.15   $177.10  
  Purchase #4 $235.27   12.624%   $264.9705   $264.97   $264.95   $265.00  
  Purchase #5 $66.83   9.485%   $73.1688   $73.17   $73.15   $73.20  
  Purchase #6 $216.41   12.802%   $244.1148   $244.11   $244.10   $244.10  
  Purchase #7 $150.60   8.582%   $163.5245   $163.52   $163.50   $163.50  
  7 purchase totals = $1,136.73       $1,260.0441   $1,260.04   $1,260.00   $1,260.00