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	$123.87	12.223%	$139.0106	$139.01	$139.00	$139.00
Purchase #2	$175.47	10.245%	$193.4469	$193.45	$193.45	$193.40
Purchase #3	$83.69	8.732%	$90.9978	$91.00	$91.00	$91.00
Purchase #4	$29.50	8.849%	$32.1105	$32.11	$32.10	$32.10
Purchase #5	$146.92	12.749%	$165.6508	$165.65	$165.65	$165.70
Purchase #6	$247.56	11.445%	$275.8932	$275.89	$275.90	$275.90
Purchase #7	$165.85	6.123%	$176.005	$176.01	$176.00	$176.00
7 purchase totals =	$972.86		$1,073.1148	$1,073.12	$1,073.10	$1,073.10