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	$130.47	13.612%	$148.2296	$148.23	$148.25	$148.20
Purchase #2	$160.83	7.102%	$172.2521	$172.25	$172.25	$172.30
Purchase #3	$230.56	9.220%	$251.8176	$251.82	$251.80	$251.80
Purchase #4	$149.26	10.508%	$164.9442	$164.94	$164.95	$164.90
Purchase #5	$190.27	13.267%	$215.5131	$215.51	$215.50	$215.50
Purchase #6	$162.90	11.648%	$181.8746	$181.87	$181.85	$181.90
Purchase #7	$101.44	6.614%	$108.1492	$108.15	$108.15	$108.10
7 purchase totals =	$1,125.73		$1,242.7804	$1,242.77	$1,242.75	$1,242.70