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	$229.93	12.647%	$259.0092	$259.01	$259.00	$259.00
Purchase #2	$92.45	13.603%	$105.026	$105.03	$105.05	$105.00
Purchase #3	$70.88	7.427%	$76.1443	$76.14	$76.15	$76.10
Purchase #4	$125.27	10.127%	$137.9561	$137.96	$137.95	$138.00
Purchase #5	$56.93	4.224%	$59.3347	$59.33	$59.35	$59.30
Purchase #6	$195.90	9.604%	$214.7142	$214.71	$214.70	$214.70
Purchase #7	$36.69	11.129%	$40.7732	$40.77	$40.75	$40.80
7 purchase totals =	$808.05		$892.9577	$892.95	$892.95	$892.90