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 $72.92   8.707%   $79.2691   $79.27   $79.25   $79.30  
  Purchase #2 $56.60   7.586%   $60.8937   $60.89   $60.90   $60.90  
  Purchase #3 $200.43   6.342%   $213.1413   $213.14   $213.15   $213.10  
  Purchase #4 $82.46   9.395%   $90.2071   $90.21   $90.20   $90.20  
  Purchase #5 $139.68   9.298%   $152.6674   $152.67   $152.65   $152.70  
  Purchase #6 $135.88   9.456%   $148.7288   $148.73   $148.75   $148.70  
  Purchase #7 $183.96   11.486%   $205.0896   $205.09   $205.10   $205.10  
  7 purchase totals = $871.93       $949.9970   $950.00   $950.00   $950.00