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	$248.40	9.292%	$271.4813	$271.48	$271.50	$271.50
Purchase #2	$211.91	4.576%	$221.607	$221.61	$221.60	$221.60
Purchase #3	$72.82	5.706%	$76.9751	$76.98	$77.00	$77.00
Purchase #4	$142.49	6.195%	$151.3173	$151.32	$151.30	$151.30
Purchase #5	$236.94	13.810%	$269.6614	$269.66	$269.65	$269.70
Purchase #6	$64.43	12.333%	$72.3762	$72.38	$72.40	$72.40
Purchase #7	$84.31	11.586%	$94.0782	$94.08	$94.10	$94.10
7 purchase totals =	$1,061.30		$1,157.4965	$1,157.51	$1,157.55	$1,157.60