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 $184.44   5.871%   $195.2685   $195.27   $195.25   $195.30  
  Purchase #2 $228.73   6.618%   $243.8674   $243.87   $243.85   $243.90  
  Purchase #3 $245.96   11.186%   $273.4731   $273.47   $273.45   $273.50  
  Purchase #4 $48.51   3.539%   $50.2268   $50.23   $50.25   $50.20  
  Purchase #5 $134.71   11.221%   $149.8258   $149.83   $149.85   $149.80  
  Purchase #6 $64.73   4.232%   $67.4694   $67.47   $67.45   $67.50  
  Purchase #7 $72.95   4.431%   $76.1824   $76.18   $76.20   $76.20  
  7 purchase totals = $980.03       $1,056.3134   $1,056.32   $1,056.30   $1,056.40