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 $32.60   6.582%   $34.7457   $34.75   $34.75   $34.70  
  Purchase #2 $103.83   8.495%   $112.6504   $112.65   $112.65   $112.70  
  Purchase #3 $205.42   5.605%   $216.9338   $216.93   $216.95   $216.90  
  Purchase #4 $65.35   8.231%   $70.729   $70.73   $70.75   $70.70  
  Purchase #5 $151.26   6.155%   $160.5701   $160.57   $160.55   $160.60  
  Purchase #6 $193.71   11.863%   $216.6898   $216.69   $216.70   $216.70  
  Purchase #7 $17.82   6.435%   $18.9667   $18.97   $18.95   $19.00  
  7 purchase totals = $769.99       $831.2855   $831.29   $831.30   $831.30