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 $61.71   5.714%   $65.2361   $65.24   $65.25   $65.20  
  Purchase #2 $212.62   13.514%   $241.3535   $241.35   $241.35   $241.40  
  Purchase #3 $102.70   4.698%   $107.5248   $107.52   $107.50   $107.50  
  Purchase #4 $171.91   7.185%   $184.2617   $184.26   $184.25   $184.30  
  Purchase #5 $182.98   3.308%   $189.033   $189.03   $189.05   $189.00  
  Purchase #6 $79.25   6.337%   $84.2721   $84.27   $84.25   $84.30  
  Purchase #7 $74.41   3.277%   $76.8484   $76.85   $76.85   $76.80  
  7 purchase totals = $885.58       $948.5296   $948.52   $948.50   $948.50