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	$151.92	13.290%	$172.1102	$172.11	$172.10	$172.10
Purchase #2	$155.61	11.107%	$172.8936	$172.89	$172.90	$172.90
Purchase #3	$195.84	13.485%	$222.249	$222.25	$222.25	$222.20
Purchase #4	$164.86	4.262%	$171.8863	$171.89	$171.90	$171.90
Purchase #5	$96.86	10.618%	$107.1446	$107.14	$107.15	$107.10
Purchase #6	$238.68	13.123%	$270.002	$270.00	$270.00	$270.00
Purchase #7	$113.71	5.742%	$120.2392	$120.24	$120.25	$120.20
7 purchase totals =	$1,117.48		$1,236.5249	$1,236.52	$1,236.55	$1,236.40