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	$31.85	6.799%	$34.0155	$34.02	$34.00	$34.00
Purchase #2	$39.92	4.768%	$41.8234	$41.82	$41.80	$41.80
Purchase #3	$70.67	11.427%	$78.7455	$78.75	$78.75	$78.70
Purchase #4	$157.79	4.747%	$165.2803	$165.28	$165.30	$165.30
Purchase #5	$179.58	3.205%	$185.3355	$185.34	$185.35	$185.30
Purchase #6	$234.37	13.158%	$265.2084	$265.21	$265.20	$265.20
Purchase #7	$134.72	3.681%	$139.679	$139.68	$139.70	$139.70
7 purchase totals =	$848.90		$910.0876	$910.10	$910.10	$910.00