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	$244.86	10.292%	$270.061	$270.06	$270.05	$270.10
Purchase #2	$150.27	12.175%	$168.5654	$168.57	$168.55	$168.60
Purchase #3	$13.92	7.748%	$14.9985	$15.00	$15.00	$15.00
Purchase #4	$83.68	9.274%	$91.4405	$91.44	$91.45	$91.40
Purchase #5	$9.42	9.689%	$10.3327	$10.33	$10.35	$10.30
Purchase #6	$245.89	6.776%	$262.5515	$262.55	$262.55	$262.60
Purchase #7	$60.72	11.531%	$67.7216	$67.72	$67.70	$67.70
7 purchase totals =	$808.76		$885.6712	$885.67	$885.65	$885.70