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	$233.68	13.108%	$264.3108	$264.31	$264.30	$264.30
Purchase #2	$239.89	13.610%	$272.539	$272.54	$272.55	$272.50
Purchase #3	$73.68	9.662%	$80.799	$80.80	$80.80	$80.80
Purchase #4	$94.47	13.675%	$107.3888	$107.39	$107.40	$107.40
Purchase #5	$84.70	5.478%	$89.3399	$89.34	$89.35	$89.30
Purchase #6	$211.72	3.506%	$219.1429	$219.14	$219.15	$219.10
Purchase #7	$173.81	5.247%	$182.9298	$182.93	$182.95	$182.90
7 purchase totals =	$1,111.95		$1,216.4502	$1,216.45	$1,216.50	$1,216.30