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	$29.79	11.281%	$33.1506	$33.15	$33.15	$33.20
Purchase #2	$152.71	4.526%	$159.6217	$159.62	$159.60	$159.60
Purchase #3	$83.87	7.174%	$89.8868	$89.89	$89.90	$89.90
Purchase #4	$84.73	11.487%	$94.4629	$94.46	$94.45	$94.50
Purchase #5	$243.72	4.676%	$255.1163	$255.12	$255.10	$255.10
Purchase #6	$60.59	6.412%	$64.475	$64.48	$64.50	$64.50
Purchase #7	$23.63	3.231%	$24.3935	$24.39	$24.40	$24.40
7 purchase totals =	$679.04		$721.1068	$721.11	$721.10	$721.20