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 $5.60   7.603%   $6.0258   $6.03   $6.05   $6.00  
  Purchase #2 $216.42   11.459%   $241.2196   $241.22   $241.20   $241.20  
  Purchase #3 $72.48   3.434%   $74.969   $74.97   $74.95   $75.00  
  Purchase #4 $103.29   12.442%   $116.1413   $116.14   $116.15   $116.10  
  Purchase #5 $72.43   6.289%   $76.9851   $76.99   $77.00   $77.00  
  Purchase #6 $118.97   10.859%   $131.889   $131.89   $131.90   $131.90  
  Purchase #7 $108.68   9.452%   $118.9524   $118.95   $118.95   $119.00  
  7 purchase totals = $697.87       $766.1822   $766.19   $766.20   $766.20