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	$69.73	13.178%	$78.919	$78.92	$78.90	$78.90
Purchase #2	$201.94	13.742%	$229.6906	$229.69	$229.70	$229.70
Purchase #3	$152.86	11.360%	$170.2249	$170.22	$170.20	$170.20
Purchase #4	$46.59	7.562%	$50.1131	$50.11	$50.10	$50.10
Purchase #5	$212.45	5.475%	$224.0816	$224.08	$224.10	$224.10
Purchase #6	$97.29	3.147%	$100.3517	$100.35	$100.35	$100.40
Purchase #7	$148.70	7.146%	$159.3261	$159.33	$159.35	$159.30
7 purchase totals =	$929.56		$1,012.7070	$1,012.70	$1,012.70	$1,012.70