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	$233.78	6.572%	$249.144	$249.14	$249.15	$249.10
Purchase #2	$15.51	7.707%	$16.7054	$16.71	$16.70	$16.70
Purchase #3	$237.28	5.590%	$250.544	$250.54	$250.55	$250.50
Purchase #4	$222.44	12.797%	$250.9056	$250.91	$250.90	$250.90
Purchase #5	$7.82	7.138%	$8.3782	$8.38	$8.40	$8.40
Purchase #6	$218.90	8.866%	$238.3077	$238.31	$238.30	$238.30
Purchase #7	$129.86	4.829%	$136.1309	$136.13	$136.15	$136.10
7 purchase totals =	$1,065.59		$1,150.1158	$1,150.12	$1,150.15	$1,150.00