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	$37.78	8.459%	$40.9758	$40.98	$41.00	$41.00
Purchase #2	$42.81	5.731%	$45.2634	$45.26	$45.25	$45.30
Purchase #3	$106.72	4.658%	$111.691	$111.69	$111.70	$111.70
Purchase #4	$68.77	3.528%	$71.1962	$71.20	$71.20	$71.20
Purchase #5	$136.40	11.596%	$152.2169	$152.22	$152.20	$152.20
Purchase #6	$233.41	9.586%	$255.7847	$255.78	$255.80	$255.80
Purchase #7	$150.55	12.390%	$169.2031	$169.20	$169.20	$169.20
7 purchase totals =	$776.44		$846.3311	$846.33	$846.35	$846.40