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	$166.54	7.139%	$178.4293	$178.43	$178.45	$178.40
Purchase #2	$172.76	9.252%	$188.7438	$188.74	$188.75	$188.70
Purchase #3	$106.68	13.301%	$120.8695	$120.87	$120.85	$120.90
Purchase #4	$18.66	13.713%	$21.2188	$21.22	$21.20	$21.20
Purchase #5	$200.61	6.354%	$213.3568	$213.36	$213.35	$213.40
Purchase #6	$175.40	5.514%	$185.0716	$185.07	$185.05	$185.10
Purchase #7	$64.48	10.529%	$71.2691	$71.27	$71.25	$71.30
7 purchase totals =	$905.13		$978.9589	$978.96	$978.90	$979.00