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	$237.80	5.134%	$250.0087	$250.01	$250.00	$250.00
Purchase #2	$31.39	9.340%	$34.3218	$34.32	$34.30	$34.30
Purchase #3	$162.72	4.369%	$169.8292	$169.83	$169.85	$169.80
Purchase #4	$217.40	11.686%	$242.8054	$242.81	$242.80	$242.80
Purchase #5	$114.37	11.523%	$127.5489	$127.55	$127.55	$127.50
Purchase #6	$249.25	13.117%	$281.9441	$281.94	$281.95	$281.90
Purchase #7	$56.37	13.754%	$64.1231	$64.12	$64.10	$64.10
7 purchase totals =	$1,069.30		$1,170.5812	$1,170.58	$1,170.55	$1,170.40