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 $70.63   7.131%   $75.6666   $75.67   $75.65   $75.70  
  Purchase #2 $103.61   6.256%   $110.0918   $110.09   $110.10   $110.10  
  Purchase #3 $66.87   4.735%   $70.0363   $70.04   $70.05   $70.00  
  Purchase #4 $81.91   4.614%   $85.6893   $85.69   $85.70   $85.70  
  Purchase #5 $162.38   6.729%   $173.3066   $173.31   $173.30   $173.30  
  Purchase #6 $213.83   11.434%   $238.2793   $238.28   $238.30   $238.30  
  Purchase #7 $22.99   11.666%   $25.672   $25.67   $25.65   $25.70  
  7 purchase totals = $722.22       $778.7419   $778.75   $778.75   $778.80