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	$50.39	11.710%	$56.2907	$56.29	$56.30	$56.30
Purchase #2	$242.74	13.512%	$275.539	$275.54	$275.55	$275.50
Purchase #3	$30.48	8.666%	$33.1214	$33.12	$33.10	$33.10
Purchase #4	$19.69	4.559%	$20.5877	$20.59	$20.60	$20.60
Purchase #5	$48.58	7.471%	$52.2094	$52.21	$52.20	$52.20
Purchase #6	$131.36	13.401%	$148.9636	$148.96	$148.95	$149.00
Purchase #7	$97.70	9.442%	$106.9248	$106.92	$106.90	$106.90
7 purchase totals =	$620.94		$693.6366	$693.63	$693.60	$693.60