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	$85.31	10.795%	$94.5192	$94.52	$94.50	$94.50
Purchase #2	$228.34	4.250%	$238.0445	$238.04	$238.05	$238.00
Purchase #3	$25.51	5.694%	$26.9625	$26.96	$26.95	$27.00
Purchase #4	$10.63	11.557%	$11.8585	$11.86	$11.85	$11.90
Purchase #5	$209.30	11.591%	$233.56	$233.56	$233.55	$233.60
Purchase #6	$106.68	4.387%	$111.3601	$111.36	$111.35	$111.40
Purchase #7	$92.83	7.184%	$99.4989	$99.50	$99.50	$99.50
7 purchase totals =	$758.60		$815.8037	$815.80	$815.75	$815.90