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 $209.84   12.140%   $235.3146   $235.31   $235.30   $235.30  
  Purchase #2 $38.32   13.318%   $43.4235   $43.42   $43.40   $43.40  
  Purchase #3 $34.32   3.753%   $35.608   $35.61   $35.60   $35.60  
  Purchase #4 $143.73   5.573%   $151.7401   $151.74   $151.75   $151.70  
  Purchase #5 $188.76   13.197%   $213.6707   $213.67   $213.65   $213.70  
  Purchase #6 $159.34   9.341%   $174.2239   $174.22   $174.20   $174.20  
  Purchase #7 $88.34   8.742%   $96.0627   $96.06   $96.05   $96.10  
  7 purchase totals = $862.65       $950.0435   $950.03   $949.95   $950.00