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	$127.83	6.470%	$136.1006	$136.10	$136.10	$136.10
Purchase #2	$242.29	3.519%	$250.8162	$250.82	$250.80	$250.80
Purchase #3	$227.64	6.701%	$242.8942	$242.89	$242.90	$242.90
Purchase #4	$137.58	6.245%	$146.1719	$146.17	$146.15	$146.20
Purchase #5	$40.51	7.141%	$43.4028	$43.40	$43.40	$43.40
Purchase #6	$147.80	13.437%	$167.6599	$167.66	$167.65	$167.70
Purchase #7	$250.94	8.810%	$273.0478	$273.05	$273.05	$273.00
7 purchase totals =	$1,174.59		$1,260.0934	$1,260.09	$1,260.05	$1,260.10