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	$130.28	4.541%	$136.196	$136.20	$136.20	$136.20
Purchase #2	$205.64	3.640%	$213.1253	$213.13	$213.15	$213.10
Purchase #3	$115.78	3.140%	$119.4155	$119.42	$119.40	$119.40
Purchase #4	$228.85	12.816%	$258.1794	$258.18	$258.20	$258.20
Purchase #5	$124.75	10.533%	$137.8899	$137.89	$137.90	$137.90
Purchase #6	$111.82	10.639%	$123.7165	$123.72	$123.70	$123.70
Purchase #7	$78.61	6.761%	$83.9248	$83.92	$83.90	$83.90
7 purchase totals =	$995.73		$1,072.4474	$1,072.46	$1,072.45	$1,072.40