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 $60.94   8.260%   $65.9736   $65.97   $65.95   $66.00  
  Purchase #2 $205.30   6.405%   $218.4495   $218.45   $218.45   $218.40  
  Purchase #3 $158.51   12.411%   $178.1827   $178.18   $178.20   $178.20  
  Purchase #4 $75.71   9.766%   $83.1038   $83.10   $83.10   $83.10  
  Purchase #5 $9.26   8.258%   $10.0247   $10.02   $10.00   $10.00  
  Purchase #6 $21.90   10.336%   $24.1636   $24.16   $24.15   $24.20  
  Purchase #7 $188.75   6.479%   $200.9791   $200.98   $201.00   $201.00  
  7 purchase totals = $720.37       $780.8770   $780.86   $780.85   $780.90