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	$116.44	12.410%	$130.8902	$130.89	$130.90	$130.90
Purchase #2	$238.60	13.359%	$270.4746	$270.47	$270.45	$270.50
Purchase #3	$124.33	8.472%	$134.8632	$134.86	$134.85	$134.90
Purchase #4	$224.89	11.676%	$251.1482	$251.15	$251.15	$251.10
Purchase #5	$181.50	4.364%	$189.4207	$189.42	$189.40	$189.40
Purchase #6	$91.82	8.730%	$99.8359	$99.84	$99.85	$99.80
Purchase #7	$39.72	11.747%	$44.3859	$44.39	$44.40	$44.40
7 purchase totals =	$1,017.30		$1,121.0187	$1,121.02	$1,121.00	$1,121.00