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	$108.42	13.709%	$123.2833	$123.28	$123.30	$123.30
Purchase #2	$37.44	4.632%	$39.1742	$39.17	$39.15	$39.20
Purchase #3	$145.85	4.415%	$152.2893	$152.29	$152.30	$152.30
Purchase #4	$92.89	5.213%	$97.7324	$97.73	$97.75	$97.70
Purchase #5	$95.52	13.498%	$108.4133	$108.41	$108.40	$108.40
Purchase #6	$223.94	5.714%	$236.7359	$236.74	$236.75	$236.70
Purchase #7	$57.38	13.126%	$64.9117	$64.91	$64.90	$64.90
7 purchase totals =	$761.44		$822.5401	$822.53	$822.55	$822.50