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	$124.75	3.319%	$128.8905	$128.89	$128.90	$128.90
Purchase #2	$208.59	3.685%	$216.2765	$216.28	$216.30	$216.30
Purchase #3	$137.41	6.277%	$146.0352	$146.04	$146.05	$146.00
Purchase #4	$199.52	11.571%	$222.6065	$222.61	$222.60	$222.60
Purchase #5	$183.88	12.667%	$207.1721	$207.17	$207.15	$207.20
Purchase #6	$78.65	5.481%	$82.9608	$82.96	$82.95	$83.00
Purchase #7	$247.52	8.398%	$268.3067	$268.31	$268.30	$268.30
7 purchase totals =	$1,180.32		$1,272.2483	$1,272.26	$1,272.25	$1,272.30