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 $237.66   6.655%   $253.4763   $253.48   $253.50   $253.50  
  Purchase #2 $125.41   12.384%   $140.9408   $140.94   $140.95   $140.90  
  Purchase #3 $14.91   9.138%   $16.2725   $16.27   $16.25   $16.30  
  Purchase #4 $177.36   12.215%   $199.0245   $199.02   $199.00   $199.00  
  Purchase #5 $43.35   7.254%   $46.4946   $46.49   $46.50   $46.50  
  Purchase #6 $173.57   9.510%   $190.0765   $190.08   $190.10   $190.10  
  Purchase #7 $235.85   4.626%   $246.7604   $246.76   $246.75   $246.80  
  7 purchase totals = $1,008.11       $1,093.0456   $1,093.04   $1,093.05   $1,093.10