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	$30.52	7.820%	$32.9067	$32.91	$32.90	$32.90
Purchase #2	$225.82	12.503%	$254.0543	$254.05	$254.05	$254.10
Purchase #3	$96.97	9.863%	$106.5342	$106.53	$106.55	$106.50
Purchase #4	$124.32	10.674%	$137.5899	$137.59	$137.60	$137.60
Purchase #5	$123.43	13.141%	$139.6499	$139.65	$139.65	$139.60
Purchase #6	$225.84	7.376%	$242.498	$242.50	$242.50	$242.50
Purchase #7	$92.62	8.279%	$100.288	$100.29	$100.30	$100.30
7 purchase totals =	$919.52		$1,013.5210	$1,013.52	$1,013.55	$1,013.50