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 $92.64   4.478%   $96.7884   $96.79   $96.80   $96.80  
  Purchase #2 $237.30   11.139%   $263.7328   $263.73   $263.75   $263.70  
  Purchase #3 $224.72   5.601%   $237.3066   $237.31   $237.30   $237.30  
  Purchase #4 $82.67   11.249%   $91.9695   $91.97   $91.95   $92.00  
  Purchase #5 $170.33   3.454%   $176.2132   $176.21   $176.20   $176.20  
  Purchase #6 $83.65   8.800%   $91.0112   $91.01   $91.00   $91.00  
  Purchase #7 $12.31   5.142%   $12.943   $12.94   $12.95   $12.90  
  7 purchase totals = $903.62       $969.9647   $969.96   $969.95   $969.90