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	$33.35	5.399%	$35.1506	$35.15	$35.15	$35.20
Purchase #2	$150.85	13.565%	$171.3128	$171.31	$171.30	$171.30
Purchase #3	$53.80	11.853%	$60.1769	$60.18	$60.20	$60.20
Purchase #4	$223.69	9.779%	$245.5646	$245.56	$245.55	$245.60
Purchase #5	$34.93	10.638%	$38.6459	$38.65	$38.65	$38.60
Purchase #6	$214.61	4.740%	$224.7825	$224.78	$224.80	$224.80
Purchase #7	$41.25	3.792%	$42.8142	$42.81	$42.80	$42.80
7 purchase totals =	$752.48		$818.4475	$818.44	$818.45	$818.50