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 $50.47   8.372%   $54.6953   $54.70   $54.70   $54.70  
  Purchase #2 $127.44   12.559%   $143.4452   $143.45   $143.45   $143.40  
  Purchase #3 $63.57   8.811%   $69.1712   $69.17   $69.15   $69.20  
  Purchase #4 $142.94   7.621%   $153.8335   $153.83   $153.85   $153.80  
  Purchase #5 $19.36   4.334%   $20.1991   $20.20   $20.20   $20.20  
  Purchase #6 $176.99   10.152%   $194.958   $194.96   $194.95   $195.00  
  Purchase #7 $181.87   7.390%   $195.3102   $195.31   $195.30   $195.30  
  7 purchase totals = $762.64       $831.6125   $831.62   $831.60   $831.60