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 $58.76   12.222%   $65.9416   $65.94   $65.95   $65.90  
  Purchase #2 $215.85   10.251%   $237.9768   $237.98   $238.00   $238.00  
  Purchase #3 $155.65   10.375%   $171.7987   $171.80   $171.80   $171.80  
  Purchase #4 $59.59   11.137%   $66.2265   $66.23   $66.25   $66.20  
  Purchase #5 $119.38   7.183%   $127.9551   $127.96   $127.95   $128.00  
  Purchase #6 $231.57   8.843%   $252.0477   $252.05   $252.05   $252.00  
  Purchase #7 $15.33   10.774%   $16.9817   $16.98   $17.00   $17.00  
  7 purchase totals = $856.13       $938.9281   $938.94   $939.00   $938.90