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 $69.26   5.441%   $73.0284   $73.03   $73.05   $73.00  
  Purchase #2 $234.88   9.349%   $256.8389   $256.84   $256.85   $256.80  
  Purchase #3 $207.29   11.774%   $231.6963   $231.70   $231.70   $231.70  
  Purchase #4 $124.68   3.862%   $129.4951   $129.50   $129.50   $129.50  
  Purchase #5 $42.93   8.271%   $46.4807   $46.48   $46.50   $46.50  
  Purchase #6 $219.97   9.288%   $240.4008   $240.40   $240.40   $240.40  
  Purchase #7 $154.72   4.481%   $161.653   $161.65   $161.65   $161.70  
  7 purchase totals = $1,053.73       $1,139.5932   $1,139.60   $1,139.65   $1,139.60