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 $60.41   12.556%   $67.9951   $68.00   $68.00   $68.00  
  Purchase #2 $195.40   10.477%   $215.8721   $215.87   $215.85   $215.90  
  Purchase #3 $166.67   7.798%   $179.6669   $179.67   $179.65   $179.70  
  Purchase #4 $213.34   10.426%   $235.5828   $235.58   $235.60   $235.60  
  Purchase #5 $37.37   3.658%   $38.737   $38.74   $38.75   $38.70  
  Purchase #6 $170.25   3.389%   $176.0198   $176.02   $176.00   $176.00  
  Purchase #7 $40.78   7.821%   $43.9694   $43.97   $43.95   $44.00  
  7 purchase totals = $884.22       $957.8431   $957.85   $957.80   $957.90