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	$18.54	9.284%	$20.2613	$20.26	$20.25	$20.30
Purchase #2	$134.36	7.198%	$144.0312	$144.03	$144.05	$144.00
Purchase #3	$92.85	6.765%	$99.1313	$99.13	$99.15	$99.10
Purchase #4	$102.43	8.605%	$111.2441	$111.24	$111.25	$111.20
Purchase #5	$155.64	7.782%	$167.7519	$167.75	$167.75	$167.80
Purchase #6	$175.59	6.675%	$187.3106	$187.31	$187.30	$187.30
Purchase #7	$93.85	11.169%	$104.3321	$104.33	$104.35	$104.30
7 purchase totals =	$773.26		$834.0625	$834.05	$834.10	$834.00