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	$69.50	13.536%	$78.9075	$78.91	$78.90	$78.90
Purchase #2	$211.69	13.431%	$240.1221	$240.12	$240.10	$240.10
Purchase #3	$221.76	9.707%	$243.2862	$243.29	$243.30	$243.30
Purchase #4	$130.55	7.294%	$140.0723	$140.07	$140.05	$140.10
Purchase #5	$9.57	13.328%	$10.8455	$10.85	$10.85	$10.80
Purchase #6	$149.28	4.682%	$156.2693	$156.27	$156.25	$156.30
Purchase #7	$72.42	10.526%	$80.0429	$80.04	$80.05	$80.00
7 purchase totals =	$864.77		$949.5458	$949.55	$949.50	$949.50