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	$227.41	12.144%	$255.0267	$255.03	$255.05	$255.00
Purchase #2	$38.78	9.747%	$42.5599	$42.56	$42.55	$42.60
Purchase #3	$122.52	8.823%	$133.3299	$133.33	$133.35	$133.30
Purchase #4	$40.43	13.426%	$45.8581	$45.86	$45.85	$45.90
Purchase #5	$148.53	7.562%	$159.7618	$159.76	$159.75	$159.80
Purchase #6	$32.69	12.586%	$36.8044	$36.80	$36.80	$36.80
Purchase #7	$86.34	10.701%	$95.5792	$95.58	$95.60	$95.60
7 purchase totals =	$696.70		$768.9200	$768.92	$768.95	$769.00