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 $45.84   12.431%   $51.5384   $51.54   $51.55   $51.50  
  Purchase #2 $110.27   8.423%   $119.558   $119.56   $119.55   $119.60  
  Purchase #3 $239.89   9.612%   $262.9482   $262.95   $262.95   $262.90  
  Purchase #4 $88.33   12.532%   $99.3995   $99.40   $99.40   $99.40  
  Purchase #5 $212.49   13.354%   $240.8659   $240.87   $240.85   $240.90  
  Purchase #6 $224.92   12.698%   $253.4803   $253.48   $253.50   $253.50  
  Purchase #7 $197.30   5.709%   $208.5639   $208.56   $208.55   $208.60  
  7 purchase totals = $1,119.04       $1,236.3542   $1,236.36   $1,236.35   $1,236.40