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	$109.78	4.659%	$114.8947	$114.89	$114.90	$114.90
Purchase #2	$108.67	10.684%	$120.2803	$120.28	$120.30	$120.30
Purchase #3	$173.74	10.834%	$192.563	$192.56	$192.55	$192.60
Purchase #4	$227.79	6.427%	$242.4301	$242.43	$242.45	$242.40
Purchase #5	$146.41	3.205%	$151.1024	$151.10	$151.10	$151.10
Purchase #6	$41.65	3.404%	$43.0678	$43.07	$43.05	$43.10
Purchase #7	$206.34	11.475%	$230.0175	$230.02	$230.00	$230.00
7 purchase totals =	$1,014.38		$1,094.3558	$1,094.35	$1,094.35	$1,094.40