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	$96.56	3.601%	$100.0371	$100.04	$100.05	$100.00
Purchase #2	$138.50	6.553%	$147.5759	$147.58	$147.60	$147.60
Purchase #3	$85.42	5.209%	$89.8695	$89.87	$89.85	$89.90
Purchase #4	$97.72	3.845%	$101.4773	$101.48	$101.50	$101.50
Purchase #5	$41.29	3.829%	$42.871	$42.87	$42.85	$42.90
Purchase #6	$165.45	9.218%	$180.7012	$180.70	$180.70	$180.70
Purchase #7	$174.52	11.839%	$195.1814	$195.18	$195.20	$195.20
7 purchase totals =	$799.46		$857.7134	$857.72	$857.75	$857.80