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	$32.32	12.205%	$36.2647	$36.26	$36.25	$36.30
Purchase #2	$177.30	4.596%	$185.4487	$185.45	$185.45	$185.40
Purchase #3	$213.29	9.350%	$233.2326	$233.23	$233.25	$233.20
Purchase #4	$82.61	4.824%	$86.5951	$86.60	$86.60	$86.60
Purchase #5	$35.66	13.686%	$40.5404	$40.54	$40.55	$40.50
Purchase #6	$209.82	4.486%	$219.2325	$219.23	$219.25	$219.20
Purchase #7	$21.47	3.653%	$22.2543	$22.25	$22.25	$22.30
7 purchase totals =	$772.47		$823.5683	$823.56	$823.60	$823.50