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 $218.96   10.776%   $242.5551   $242.56   $242.55   $242.60  
  Purchase #2 $213.44   10.544%   $235.9451   $235.95   $235.95   $235.90  
  Purchase #3 $218.50   13.441%   $247.8686   $247.87   $247.85   $247.90  
  Purchase #4 $49.34   12.454%   $55.4848   $55.48   $55.50   $55.50  
  Purchase #5 $94.51   10.459%   $104.3948   $104.39   $104.40   $104.40  
  Purchase #6 $127.27   12.519%   $143.2029   $143.20   $143.20   $143.20  
  Purchase #7 $231.52   5.181%   $243.5151   $243.52   $243.50   $243.50  
  7 purchase totals = $1,153.54       $1,272.9664   $1,272.97   $1,272.95   $1,273.00