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	$100.84	4.629%	$105.5079	$105.51	$105.50	$105.50
Purchase #2	$243.98	13.695%	$277.3931	$277.39	$277.40	$277.40
Purchase #3	$212.73	11.777%	$237.7832	$237.78	$237.80	$237.80
Purchase #4	$17.48	6.198%	$18.5634	$18.56	$18.55	$18.60
Purchase #5	$64.76	10.201%	$71.3662	$71.37	$71.35	$71.40
Purchase #6	$87.94	4.158%	$91.5965	$91.60	$91.60	$91.60
Purchase #7	$85.71	10.754%	$94.9273	$94.93	$94.95	$94.90
7 purchase totals =	$813.44		$897.1376	$897.14	$897.15	$897.20