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	$93.55	13.620%	$106.2915	$106.29	$106.30	$106.30
Purchase #2	$82.65	8.730%	$89.8653	$89.87	$89.85	$89.90
Purchase #3	$42.61	8.318%	$46.1543	$46.15	$46.15	$46.20
Purchase #4	$169.65	3.452%	$175.5063	$175.51	$175.50	$175.50
Purchase #5	$86.59	3.360%	$89.4994	$89.50	$89.50	$89.50
Purchase #6	$84.67	10.149%	$93.2632	$93.26	$93.25	$93.30
Purchase #7	$22.77	11.552%	$25.4004	$25.40	$25.40	$25.40
7 purchase totals =	$582.49		$625.9804	$625.98	$625.95	$626.10