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	$91.74	9.332%	$100.3012	$100.30	$100.30	$100.30
Purchase #2	$172.32	4.117%	$179.4144	$179.41	$179.40	$179.40
Purchase #3	$105.76	6.159%	$112.2738	$112.27	$112.25	$112.30
Purchase #4	$235.35	8.530%	$255.4254	$255.43	$255.45	$255.40
Purchase #5	$132.32	11.712%	$147.8173	$147.82	$147.80	$147.80
Purchase #6	$18.44	11.442%	$20.5499	$20.55	$20.55	$20.50
Purchase #7	$202.67	9.347%	$221.6136	$221.61	$221.60	$221.60
7 purchase totals =	$958.60		$1,037.3956	$1,037.39	$1,037.35	$1,037.30