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 $48.69   5.115%   $51.1805   $51.18   $51.20   $51.20  
  Purchase #2 $24.81   5.421%   $26.155   $26.16   $26.15   $26.20  
  Purchase #3 $136.36   7.559%   $146.6675   $146.67   $146.65   $146.70  
  Purchase #4 $195.76   4.324%   $204.2247   $204.22   $204.20   $204.20  
  Purchase #5 $238.73   4.204%   $248.7662   $248.77   $248.75   $248.80  
  Purchase #6 $81.97   5.417%   $86.4103   $86.41   $86.40   $86.40  
  Purchase #7 $205.42   11.229%   $228.4866   $228.49   $228.50   $228.50  
  7 purchase totals = $931.74       $991.8908   $991.90   $991.85   $992.00