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	$6.63	11.174%	$7.3708	$7.37	$7.35	$7.40
Purchase #2	$55.68	4.452%	$58.1589	$58.16	$58.15	$58.20
Purchase #3	$56.64	4.675%	$59.2879	$59.29	$59.30	$59.30
Purchase #4	$156.25	5.380%	$164.6563	$164.66	$164.65	$164.70
Purchase #5	$231.79	13.605%	$263.325	$263.33	$263.35	$263.30
Purchase #6	$247.88	6.817%	$264.778	$264.78	$264.80	$264.80
Purchase #7	$144.94	13.657%	$164.7345	$164.73	$164.75	$164.70
7 purchase totals =	$899.81		$982.3114	$982.32	$982.35	$982.40