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	$115.46	12.796%	$130.2343	$130.23	$130.25	$130.20
Purchase #2	$164.55	11.510%	$183.4897	$183.49	$183.50	$183.50
Purchase #3	$60.82	13.205%	$68.8513	$68.85	$68.85	$68.90
Purchase #4	$118.88	4.804%	$124.591	$124.59	$124.60	$124.60
Purchase #5	$84.34	11.196%	$93.7827	$93.78	$93.80	$93.80
Purchase #6	$245.31	13.702%	$278.9224	$278.92	$278.90	$278.90
Purchase #7	$127.68	7.243%	$136.9279	$136.93	$136.95	$136.90
7 purchase totals =	$917.04		$1,016.7993	$1,016.79	$1,016.85	$1,016.80