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	$121.75	8.139%	$131.6592	$131.66	$131.65	$131.70
Purchase #2	$151.45	11.398%	$168.7123	$168.71	$168.70	$168.70
Purchase #3	$133.83	12.867%	$151.0499	$151.05	$151.05	$151.00
Purchase #4	$99.51	9.848%	$109.3097	$109.31	$109.30	$109.30
Purchase #5	$224.45	9.175%	$245.0433	$245.04	$245.05	$245.00
Purchase #6	$157.78	5.559%	$166.551	$166.55	$166.55	$166.60
Purchase #7	$118.48	13.507%	$134.4831	$134.48	$134.50	$134.50
7 purchase totals =	$1,007.25		$1,106.8085	$1,106.80	$1,106.80	$1,106.80