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 $241.95   7.563%   $260.2487   $260.25   $260.25   $260.20  
  Purchase #2 $110.56   11.162%   $122.9007   $122.90   $122.90   $122.90  
  Purchase #3 $66.31   6.119%   $70.3675   $70.37   $70.35   $70.40  
  Purchase #4 $121.35   13.179%   $137.3427   $137.34   $137.35   $137.30  
  Purchase #5 $95.95   13.302%   $108.7133   $108.71   $108.70   $108.70  
  Purchase #6 $38.64   5.469%   $40.7532   $40.75   $40.75   $40.80  
  Purchase #7 $26.87   11.369%   $29.9249   $29.92   $29.90   $29.90  
  7 purchase totals = $701.63       $770.2510   $770.24   $770.20   $770.20