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	$72.73	9.507%	$79.6444	$79.64	$79.65	$79.60
Purchase #2	$57.86	13.593%	$65.7249	$65.72	$65.70	$65.70
Purchase #3	$173.89	11.488%	$193.8665	$193.87	$193.85	$193.90
Purchase #4	$40.40	4.249%	$42.1166	$42.12	$42.10	$42.10
Purchase #5	$164.32	9.370%	$179.7168	$179.72	$179.70	$179.70
Purchase #6	$28.69	13.508%	$32.5654	$32.57	$32.55	$32.60
Purchase #7	$144.29	3.649%	$149.5551	$149.56	$149.55	$149.60
7 purchase totals =	$682.18		$743.1897	$743.20	$743.10	$743.20