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 $192.66   8.323%   $208.6951   $208.70   $208.70   $208.70  
  Purchase #2 $96.39   11.212%   $107.1972   $107.20   $107.20   $107.20  
  Purchase #3 $36.74   6.174%   $39.0083   $39.01   $39.00   $39.00  
  Purchase #4 $22.43   13.196%   $25.3899   $25.39   $25.40   $25.40  
  Purchase #5 $159.80   10.844%   $177.1287   $177.13   $177.15   $177.10  
  Purchase #6 $244.92   10.853%   $271.5012   $271.50   $271.50   $271.50  
  Purchase #7 $101.69   9.316%   $111.1634   $111.16   $111.15   $111.20  
  7 purchase totals = $854.63       $940.0838   $940.09   $940.10   $940.10