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 $201.81   8.402%   $218.7661   $218.77   $218.75   $218.80  
  Purchase #2 $217.60   10.151%   $239.6886   $239.69   $239.70   $239.70  
  Purchase #3 $60.52   5.306%   $63.7312   $63.73   $63.75   $63.70  
  Purchase #4 $47.39   11.762%   $52.964   $52.96   $52.95   $53.00  
  Purchase #5 $96.50   4.427%   $100.7721   $100.77   $100.75   $100.80  
  Purchase #6 $247.62   10.432%   $273.4517   $273.45   $273.45   $273.50  
  Purchase #7 $12.64   6.840%   $13.5046   $13.50   $13.50   $13.50  
  7 purchase totals = $884.08       $962.8783   $962.87   $962.85   $963.00