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	$87.63	12.553%	$98.6302	$98.63	$98.65	$98.60
Purchase #2	$240.57	11.367%	$267.9156	$267.92	$267.90	$267.90
Purchase #3	$120.64	11.539%	$134.5606	$134.56	$134.55	$134.60
Purchase #4	$58.71	10.160%	$64.6749	$64.67	$64.65	$64.70
Purchase #5	$147.44	3.317%	$152.3306	$152.33	$152.35	$152.30
Purchase #6	$246.74	11.323%	$274.6784	$274.68	$274.70	$274.70
Purchase #7	$38.59	5.194%	$40.5944	$40.59	$40.60	$40.60
7 purchase totals =	$940.32		$1,033.3847	$1,033.38	$1,033.40	$1,033.40