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 $249.96   6.747%   $266.8248   $266.82   $266.80   $266.80  
  Purchase #2 $156.61   9.193%   $171.0072   $171.01   $171.00   $171.00  
  Purchase #3 $65.72   7.316%   $70.5281   $70.53   $70.55   $70.50  
  Purchase #4 $60.39   13.806%   $68.7274   $68.73   $68.75   $68.70  
  Purchase #5 $244.32   7.610%   $262.9128   $262.91   $262.90   $262.90  
  Purchase #6 $149.29   3.751%   $154.8899   $154.89   $154.90   $154.90  
  Purchase #7 $161.74   5.370%   $170.4254   $170.43   $170.45   $170.40  
  7 purchase totals = $1,088.03       $1,165.3156   $1,165.32   $1,165.35   $1,165.20