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	$99.69	10.461%	$110.1186	$110.12	$110.10	$110.10
Purchase #2	$100.32	6.364%	$106.7044	$106.70	$106.70	$106.70
Purchase #3	$17.31	7.367%	$18.5852	$18.59	$18.60	$18.60
Purchase #4	$119.30	6.364%	$126.8923	$126.89	$126.90	$126.90
Purchase #5	$51.64	4.791%	$54.1141	$54.11	$54.10	$54.10
Purchase #6	$146.58	5.146%	$154.123	$154.12	$154.10	$154.10
Purchase #7	$85.46	5.286%	$89.9774	$89.98	$90.00	$90.00
7 purchase totals =	$620.30		$660.5150	$660.51	$660.50	$660.50