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 $89.94   6.387%   $95.6845   $95.68   $95.70   $95.70  
  Purchase #2 $32.78   12.346%   $36.827   $36.83   $36.85   $36.80  
  Purchase #3 $226.82   8.350%   $245.7595   $245.76   $245.75   $245.80  
  Purchase #4 $33.46   8.117%   $36.1759   $36.18   $36.20   $36.20  
  Purchase #5 $145.78   9.763%   $160.0125   $160.01   $160.00   $160.00  
  Purchase #6 $148.72   12.240%   $166.9233   $166.92   $166.90   $166.90  
  Purchase #7 $186.50   13.468%   $211.6178   $211.62   $211.60   $211.60  
  7 purchase totals = $864.00       $953.0005   $953.00   $953.00   $953.00