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	$242.27	9.581%	$265.4819	$265.48	$265.50	$265.50
Purchase #2	$113.66	6.303%	$120.824	$120.82	$120.80	$120.80
Purchase #3	$127.60	6.448%	$135.8276	$135.83	$135.85	$135.80
Purchase #4	$195.40	9.318%	$213.6074	$213.61	$213.60	$213.60
Purchase #5	$38.74	4.776%	$40.5902	$40.59	$40.60	$40.60
Purchase #6	$197.39	13.437%	$223.9133	$223.91	$223.90	$223.90
Purchase #7	$225.40	12.278%	$253.0746	$253.07	$253.05	$253.10
7 purchase totals =	$1,140.46		$1,253.3190	$1,253.31	$1,253.30	$1,253.30