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	$83.71	9.592%	$91.7395	$91.74	$91.75	$91.70
Purchase #2	$82.83	9.443%	$90.6516	$90.65	$90.65	$90.70
Purchase #3	$242.25	3.575%	$250.9104	$250.91	$250.90	$250.90
Purchase #4	$93.63	9.441%	$102.4696	$102.47	$102.45	$102.50
Purchase #5	$112.65	11.476%	$125.5777	$125.58	$125.60	$125.60
Purchase #6	$147.47	13.486%	$167.3578	$167.36	$167.35	$167.40
Purchase #7	$160.27	4.290%	$167.1456	$167.15	$167.15	$167.10
7 purchase totals =	$922.81		$995.8522	$995.86	$995.85	$995.90