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 $52.98   13.791%   $60.2865   $60.29   $60.30   $60.30  
  Purchase #2 $124.61   12.599%   $140.3096   $140.31   $140.30   $140.30  
  Purchase #3 $92.34   12.384%   $103.7754   $103.78   $103.80   $103.80  
  Purchase #4 $52.87   9.727%   $58.0127   $58.01   $58.00   $58.00  
  Purchase #5 $210.30   10.546%   $232.4782   $232.48   $232.50   $232.50  
  Purchase #6 $166.79   13.752%   $189.727   $189.73   $189.75   $189.70  
  Purchase #7 $190.92   10.230%   $210.4511   $210.45   $210.45   $210.50  
  7 purchase totals = $890.81       $995.0405   $995.05   $995.10   $995.10