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	$196.94	4.756%	$206.3065	$206.31	$206.30	$206.30
Purchase #2	$143.33	5.246%	$150.8491	$150.85	$150.85	$150.80
Purchase #3	$247.43	10.647%	$273.7739	$273.77	$273.75	$273.80
Purchase #4	$137.83	13.307%	$156.171	$156.17	$156.15	$156.20
Purchase #5	$100.72	5.370%	$106.1287	$106.13	$106.15	$106.10
Purchase #6	$18.87	12.120%	$21.157	$21.16	$21.15	$21.20
Purchase #7	$160.80	8.307%	$174.1577	$174.16	$174.15	$174.20
7 purchase totals =	$1,005.92		$1,088.5439	$1,088.55	$1,088.50	$1,088.60