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	$35.51	11.637%	$39.6423	$39.64	$39.65	$39.60
Purchase #2	$170.68	10.566%	$188.714	$188.71	$188.70	$188.70
Purchase #3	$209.29	8.682%	$227.4606	$227.46	$227.45	$227.50
Purchase #4	$209.40	6.707%	$223.4445	$223.44	$223.45	$223.40
Purchase #5	$99.87	9.408%	$109.2658	$109.27	$109.25	$109.30
Purchase #6	$185.28	10.672%	$205.0531	$205.05	$205.05	$205.10
Purchase #7	$92.29	9.260%	$100.8361	$100.84	$100.85	$100.80
7 purchase totals =	$1,002.32		$1,094.4164	$1,094.41	$1,094.40	$1,094.40