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	$120.89	12.730%	$136.2793	$136.28	$136.30	$136.30
Purchase #2	$72.73	12.815%	$82.0503	$82.05	$82.05	$82.10
Purchase #3	$188.84	10.281%	$208.2546	$208.25	$208.25	$208.30
Purchase #4	$65.82	11.708%	$73.5262	$73.53	$73.55	$73.50
Purchase #5	$160.64	13.313%	$182.026	$182.03	$182.05	$182.00
Purchase #6	$69.27	12.390%	$77.8526	$77.85	$77.85	$77.90
Purchase #7	$228.45	4.552%	$238.849	$238.85	$238.85	$238.80
7 purchase totals =	$906.64		$998.8380	$998.84	$998.90	$998.90