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	$229.39	9.166%	$250.4159	$250.42	$250.40	$250.40
Purchase #2	$20.59	13.345%	$23.3377	$23.34	$23.35	$23.30
Purchase #3	$196.61	8.525%	$213.371	$213.37	$213.35	$213.40
Purchase #4	$166.27	4.543%	$173.8236	$173.82	$173.80	$173.80
Purchase #5	$95.71	3.754%	$99.303	$99.30	$99.30	$99.30
Purchase #6	$10.81	4.798%	$11.3287	$11.33	$11.35	$11.30
Purchase #7	$124.67	5.413%	$131.4184	$131.42	$131.40	$131.40
7 purchase totals =	$844.05		$902.9983	$903.00	$902.95	$902.90