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 $91.34   5.107%   $96.0047   $96.00   $96.00   $96.00  
  Purchase #2 $208.64   10.554%   $230.6599   $230.66   $230.65   $230.70  
  Purchase #3 $26.91   12.579%   $30.295   $30.30   $30.30   $30.30  
  Purchase #4 $52.88   8.213%   $57.223   $57.22   $57.20   $57.20  
  Purchase #5 $244.64   13.289%   $277.1502   $277.15   $277.15   $277.20  
  Purchase #6 $191.37   5.160%   $201.2447   $201.24   $201.25   $201.20  
  Purchase #7 $43.60   10.259%   $48.0729   $48.07   $48.05   $48.10  
  7 purchase totals = $859.38       $940.6504   $940.64   $940.60   $940.70