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	$15.91	11.474%	$17.7355	$17.74	$17.75	$17.70
Purchase #2	$193.26	13.212%	$218.7935	$218.79	$218.80	$218.80
Purchase #3	$77.29	7.670%	$83.2181	$83.22	$83.20	$83.20
Purchase #4	$26.42	5.757%	$27.941	$27.94	$27.95	$27.90
Purchase #5	$173.81	3.516%	$179.9212	$179.92	$179.90	$179.90
Purchase #6	$37.89	11.221%	$42.1416	$42.14	$42.15	$42.10
Purchase #7	$92.73	13.456%	$105.2077	$105.21	$105.20	$105.20
7 purchase totals =	$617.31		$674.9586	$674.96	$674.95	$674.80