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 $82.54   13.855%   $93.9759   $93.98   $94.00   $94.00  
  Purchase #2 $81.68   6.554%   $87.0333   $87.03   $87.05   $87.00  
  Purchase #3 $236.57   13.387%   $268.2396   $268.24   $268.25   $268.20  
  Purchase #4 $126.53   4.396%   $132.0923   $132.09   $132.10   $132.10  
  Purchase #5 $108.54   9.693%   $119.0608   $119.06   $119.05   $119.10  
  Purchase #6 $204.80   12.255%   $229.8982   $229.90   $229.90   $229.90  
  Purchase #7 $138.75   12.262%   $155.7635   $155.76   $155.75   $155.80  
  7 purchase totals = $979.41       $1,086.0636   $1,086.06   $1,086.10   $1,086.10