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 $63.77   5.480%   $67.2646   $67.26   $67.25   $67.30  
  Purchase #2 $217.44   12.519%   $244.6613   $244.66   $244.65   $244.70  
  Purchase #3 $27.90   9.725%   $30.6133   $30.61   $30.60   $30.60  
  Purchase #4 $147.77   4.243%   $154.0399   $154.04   $154.05   $154.00  
  Purchase #5 $22.75   9.714%   $24.9599   $24.96   $24.95   $25.00  
  Purchase #6 $215.62   9.468%   $236.0349   $236.03   $236.05   $236.00  
  Purchase #7 $203.34   4.612%   $212.718   $212.72   $212.70   $212.70  
  7 purchase totals = $898.59       $970.2919   $970.28   $970.25   $970.30