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 $200.92   7.763%   $216.5174   $216.52   $216.50   $216.50  
  Purchase #2 $60.55   8.738%   $65.8409   $65.84   $65.85   $65.80  
  Purchase #3 $234.63   6.477%   $249.827   $249.83   $249.85   $249.80  
  Purchase #4 $47.29   13.578%   $53.711   $53.71   $53.70   $53.70  
  Purchase #5 $113.94   11.838%   $127.4282   $127.43   $127.45   $127.40  
  Purchase #6 $173.25   9.600%   $189.882   $189.88   $189.90   $189.90  
  Purchase #7 $84.41   9.394%   $92.3395   $92.34   $92.35   $92.30  
  7 purchase totals = $914.99       $995.5460   $995.55   $995.60   $995.40