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	$116.53	6.560%	$124.1744	$124.17	$124.15	$124.20
Purchase #2	$213.82	11.476%	$238.358	$238.36	$238.35	$238.40
Purchase #3	$155.44	13.385%	$176.2456	$176.25	$176.25	$176.20
Purchase #4	$143.93	10.777%	$159.4413	$159.44	$159.45	$159.40
Purchase #5	$172.60	7.424%	$185.4138	$185.41	$185.40	$185.40
Purchase #6	$224.69	6.166%	$238.5444	$238.54	$238.55	$238.50
Purchase #7	$217.56	9.496%	$238.2195	$238.22	$238.20	$238.20
7 purchase totals =	$1,244.57		$1,360.3970	$1,360.39	$1,360.35	$1,360.30