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	$169.57	10.456%	$187.3002	$187.30	$187.30	$187.30
Purchase #2	$207.68	12.201%	$233.019	$233.02	$233.00	$233.00
Purchase #3	$247.95	12.451%	$278.8223	$278.82	$278.80	$278.80
Purchase #4	$224.85	11.618%	$250.9731	$250.97	$250.95	$251.00
Purchase #5	$82.27	8.350%	$89.1395	$89.14	$89.15	$89.10
Purchase #6	$130.26	5.745%	$137.7434	$137.74	$137.75	$137.70
Purchase #7	$162.30	12.337%	$182.323	$182.32	$182.30	$182.30
7 purchase totals =	$1,224.88		$1,359.3205	$1,359.31	$1,359.25	$1,359.20