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 $60.61   9.743%   $66.5152   $66.52   $66.50   $66.50  
  Purchase #2 $224.95   13.200%   $254.6434   $254.64   $254.65   $254.60  
  Purchase #3 $33.32   8.254%   $36.0702   $36.07   $36.05   $36.10  
  Purchase #4 $104.39   10.846%   $115.7121   $115.71   $115.70   $115.70  
  Purchase #5 $59.66   10.464%   $65.9028   $65.90   $65.90   $65.90  
  Purchase #6 $182.48   10.569%   $201.7663   $201.77   $201.75   $201.80  
  Purchase #7 $150.68   11.783%   $168.4346   $168.43   $168.45   $168.40  
  7 purchase totals = $816.09       $909.0446   $909.04   $909.00   $909.00