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	$133.61	11.750%	$149.3092	$149.31	$149.30	$149.30
Purchase #2	$64.56	5.184%	$67.9068	$67.91	$67.90	$67.90
Purchase #3	$167.90	10.119%	$184.8898	$184.89	$184.90	$184.90
Purchase #4	$82.51	13.534%	$93.6769	$93.68	$93.70	$93.70
Purchase #5	$97.93	8.131%	$105.8927	$105.89	$105.90	$105.90
Purchase #6	$126.52	10.121%	$139.3251	$139.33	$139.35	$139.30
Purchase #7	$52.57	11.487%	$58.6087	$58.61	$58.60	$58.60
7 purchase totals =	$725.60		$799.6092	$799.62	$799.65	$799.60