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 $91.71   4.717%   $96.036   $96.04   $96.05   $96.00  
  Purchase #2 $30.63   13.776%   $34.8496   $34.85   $34.85   $34.80  
  Purchase #3 $65.29   8.201%   $70.6444   $70.64   $70.65   $70.60  
  Purchase #4 $12.88   6.730%   $13.7468   $13.75   $13.75   $13.70  
  Purchase #5 $209.52   13.571%   $237.954   $237.95   $237.95   $238.00  
  Purchase #6 $245.65   12.157%   $275.5137   $275.51   $275.50   $275.50  
  Purchase #7 $175.39   9.606%   $192.238   $192.24   $192.25   $192.20  
  7 purchase totals = $831.07       $920.9825   $920.98   $921.00   $920.80