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	$101.82	11.122%	$113.1444	$113.14	$113.15	$113.10
Purchase #2	$66.67	6.560%	$71.0436	$71.04	$71.05	$71.00
Purchase #3	$142.90	4.350%	$149.1162	$149.12	$149.10	$149.10
Purchase #4	$208.73	4.802%	$218.7532	$218.75	$218.75	$218.80
Purchase #5	$82.76	8.250%	$89.5877	$89.59	$89.60	$89.60
Purchase #6	$154.80	7.221%	$165.9781	$165.98	$166.00	$166.00
Purchase #7	$85.75	6.406%	$91.2431	$91.24	$91.25	$91.20
7 purchase totals =	$843.43		$898.8663	$898.86	$898.90	$898.80