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 $61.69   5.431%   $65.0404   $65.04   $65.05   $65.00  
  Purchase #2 $29.38   11.593%   $32.786   $32.79   $32.80   $32.80  
  Purchase #3 $95.78   11.696%   $106.9824   $106.98   $107.00   $107.00  
  Purchase #4 $153.63   5.441%   $161.989   $161.99   $162.00   $162.00  
  Purchase #5 $192.37   13.596%   $218.5246   $218.52   $218.50   $218.50  
  Purchase #6 $68.58   13.370%   $77.7491   $77.75   $77.75   $77.70  
  Purchase #7 $154.89   5.136%   $162.8452   $162.85   $162.85   $162.80  
  7 purchase totals = $756.32       $825.9167   $825.92   $825.95   $825.80