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	$245.59	11.118%	$272.8947	$272.89	$272.90	$272.90
Purchase #2	$58.76	12.353%	$66.0186	$66.02	$66.00	$66.00
Purchase #3	$77.77	13.809%	$88.5093	$88.51	$88.50	$88.50
Purchase #4	$99.60	4.190%	$103.7732	$103.77	$103.75	$103.80
Purchase #5	$219.52	10.223%	$241.9615	$241.96	$241.95	$242.00
Purchase #6	$21.79	11.331%	$24.259	$24.26	$24.25	$24.30
Purchase #7	$215.51	12.485%	$242.4164	$242.42	$242.40	$242.40
7 purchase totals =	$938.54		$1,039.8327	$1,039.83	$1,039.75	$1,039.90