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	$231.74	10.265%	$255.5281	$255.53	$255.55	$255.50
Purchase #2	$247.65	4.816%	$259.5768	$259.58	$259.60	$259.60
Purchase #3	$164.57	11.145%	$182.9113	$182.91	$182.90	$182.90
Purchase #4	$235.50	6.180%	$250.0539	$250.05	$250.05	$250.10
Purchase #5	$132.40	9.658%	$145.1872	$145.19	$145.20	$145.20
Purchase #6	$16.52	11.148%	$18.3616	$18.36	$18.35	$18.40
Purchase #7	$209.36	6.117%	$222.1666	$222.17	$222.15	$222.20
7 purchase totals =	$1,237.74		$1,333.7855	$1,333.79	$1,333.80	$1,333.90