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 $246.80   8.287%   $267.2523   $267.25   $267.25   $267.30  
  Purchase #2 $52.73   7.250%   $56.5529   $56.55   $56.55   $56.60  
  Purchase #3 $35.75   7.248%   $38.3412   $38.34   $38.35   $38.30  
  Purchase #4 $160.98   5.328%   $169.557   $169.56   $169.55   $169.60  
  Purchase #5 $180.48   13.434%   $204.7257   $204.73   $204.75   $204.70  
  Purchase #6 $215.76   12.836%   $243.455   $243.46   $243.45   $243.50  
  Purchase #7 $250.54   8.512%   $271.866   $271.87   $271.85   $271.90  
  7 purchase totals = $1,143.04       $1,251.7501   $1,251.76   $1,251.75   $1,251.90