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	$30.68	5.184%	$32.2705	$32.27	$32.25	$32.30
Purchase #2	$119.96	13.644%	$136.3273	$136.33	$136.35	$136.30
Purchase #3	$19.31	11.315%	$21.4949	$21.49	$21.50	$21.50
Purchase #4	$124.96	12.221%	$140.2314	$140.23	$140.25	$140.20
Purchase #5	$34.51	9.399%	$37.7536	$37.75	$37.75	$37.80
Purchase #6	$152.59	12.235%	$171.2594	$171.26	$171.25	$171.30
Purchase #7	$69.40	4.593%	$72.5875	$72.59	$72.60	$72.60
7 purchase totals =	$551.41		$611.9246	$611.92	$611.95	$612.00