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 $83.81   11.185%   $93.1841   $93.18   $93.20   $93.20  
  Purchase #2 $180.48   6.485%   $192.1841   $192.18   $192.20   $192.20  
  Purchase #3 $247.45   13.552%   $280.9844   $280.98   $281.00   $281.00  
  Purchase #4 $42.29   5.485%   $44.6096   $44.61   $44.60   $44.60  
  Purchase #5 $126.97   10.218%   $139.9438   $139.94   $139.95   $139.90  
  Purchase #6 $47.29   13.472%   $53.6609   $53.66   $53.65   $53.70  
  Purchase #7 $54.35   13.369%   $61.6161   $61.62   $61.60   $61.60  
  7 purchase totals = $782.64       $866.1830   $866.17   $866.20   $866.20