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	$46.76	7.854%	$50.4325	$50.43	$50.45	$50.40
Purchase #2	$140.99	3.511%	$145.9402	$145.94	$145.95	$145.90
Purchase #3	$187.89	11.194%	$208.9224	$208.92	$208.90	$208.90
Purchase #4	$146.25	10.243%	$161.2304	$161.23	$161.25	$161.20
Purchase #5	$164.26	5.213%	$172.8229	$172.82	$172.80	$172.80
Purchase #6	$159.57	3.332%	$164.8869	$164.89	$164.90	$164.90
Purchase #7	$199.75	12.110%	$223.9397	$223.94	$223.95	$223.90
7 purchase totals =	$1,045.47		$1,128.1750	$1,128.17	$1,128.20	$1,128.00