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	$25.59	10.602%	$28.3031	$28.30	$28.30	$28.30
Purchase #2	$210.65	13.653%	$239.41	$239.41	$239.40	$239.40
Purchase #3	$156.69	10.243%	$172.7398	$172.74	$172.75	$172.70
Purchase #4	$83.27	10.852%	$92.3065	$92.31	$92.30	$92.30
Purchase #5	$201.27	3.555%	$208.4251	$208.43	$208.45	$208.40
Purchase #6	$88.51	11.592%	$98.7701	$98.77	$98.75	$98.80
Purchase #7	$221.89	9.282%	$242.4858	$242.49	$242.50	$242.50
7 purchase totals =	$987.87		$1,082.4404	$1,082.45	$1,082.45	$1,082.40