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	$89.28	12.153%	$100.1302	$100.13	$100.15	$100.10
Purchase #2	$10.88	10.398%	$12.0113	$12.01	$12.00	$12.00
Purchase #3	$21.26	13.299%	$24.0874	$24.09	$24.10	$24.10
Purchase #4	$167.30	7.630%	$180.065	$180.07	$180.05	$180.10
Purchase #5	$52.36	13.111%	$59.2249	$59.22	$59.20	$59.20
Purchase #6	$157.63	11.108%	$175.1395	$175.14	$175.15	$175.10
Purchase #7	$16.44	12.714%	$18.5302	$18.53	$18.55	$18.50
7 purchase totals =	$515.15		$569.1885	$569.19	$569.20	$569.10