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	$60.74	4.185%	$63.282	$63.28	$63.30	$63.30
Purchase #2	$170.87	11.812%	$191.0532	$191.05	$191.05	$191.10
Purchase #3	$46.72	13.761%	$53.1491	$53.15	$53.15	$53.10
Purchase #4	$104.64	4.217%	$109.0527	$109.05	$109.05	$109.10
Purchase #5	$218.38	5.213%	$229.7641	$229.76	$229.75	$229.80
Purchase #6	$18.50	3.604%	$19.1667	$19.17	$19.15	$19.20
Purchase #7	$153.85	5.467%	$162.261	$162.26	$162.25	$162.30
7 purchase totals =	$773.70		$827.7288	$827.72	$827.70	$827.90