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 $61.94   5.813%   $65.5406   $65.54   $65.55   $65.50  
  Purchase #2 $106.65   12.368%   $119.8405   $119.84   $119.85   $119.80  
  Purchase #3 $228.95   9.468%   $250.627   $250.63   $250.65   $250.60  
  Purchase #4 $104.67   4.782%   $109.6753   $109.68   $109.70   $109.70  
  Purchase #5 $137.83   8.735%   $149.8695   $149.87   $149.85   $149.90  
  Purchase #6 $183.51   11.812%   $205.1862   $205.19   $205.20   $205.20  
  Purchase #7 $67.43   4.162%   $70.2364   $70.24   $70.25   $70.20  
  7 purchase totals = $890.98       $970.9755   $970.99   $971.05   $970.90