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	$146.47	13.556%	$166.3255	$166.33	$166.35	$166.30
Purchase #2	$243.80	3.851%	$253.1887	$253.19	$253.20	$253.20
Purchase #3	$89.48	11.582%	$99.8436	$99.84	$99.85	$99.80
Purchase #4	$229.33	6.233%	$243.6241	$243.62	$243.60	$243.60
Purchase #5	$136.76	9.584%	$149.8671	$149.87	$149.85	$149.90
Purchase #6	$68.41	5.847%	$72.4099	$72.41	$72.40	$72.40
Purchase #7	$32.40	7.234%	$34.7438	$34.74	$34.75	$34.70
7 purchase totals =	$946.65		$1,020.0027	$1,020.00	$1,020.00	$1,019.90