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 $51.76   4.834%   $54.2621   $54.26   $54.25   $54.30  
  Purchase #2 $55.37   9.186%   $60.4563   $60.46   $60.45   $60.50  
  Purchase #3 $88.34   7.517%   $94.9805   $94.98   $95.00   $95.00  
  Purchase #4 $232.25   3.871%   $241.2404   $241.24   $241.25   $241.20  
  Purchase #5 $175.31   12.374%   $197.0029   $197.00   $197.00   $197.00  
  Purchase #6 $84.73   8.234%   $91.7067   $91.71   $91.70   $91.70  
  Purchase #7 $115.37   6.233%   $122.561   $122.56   $122.55   $122.60  
  7 purchase totals = $803.13       $862.2099   $862.21   $862.20   $862.30