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	$17.72	3.758%	$18.3859	$18.39	$18.40	$18.40
Purchase #2	$83.48	13.433%	$94.6939	$94.69	$94.70	$94.70
Purchase #3	$124.31	3.630%	$128.8225	$128.82	$128.80	$128.80
Purchase #4	$41.64	13.427%	$47.231	$47.23	$47.25	$47.20
Purchase #5	$229.84	5.682%	$242.8995	$242.90	$242.90	$242.90
Purchase #6	$48.45	12.261%	$54.3905	$54.39	$54.40	$54.40
Purchase #7	$30.36	8.388%	$32.9066	$32.91	$32.90	$32.90
7 purchase totals =	$575.80		$619.3299	$619.33	$619.35	$619.30