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	$22.76	12.380%	$25.5777	$25.58	$25.60	$25.60
Purchase #2	$80.78	11.115%	$89.7587	$89.76	$89.75	$89.80
Purchase #3	$156.89	5.647%	$165.7496	$165.75	$165.75	$165.70
Purchase #4	$246.34	9.236%	$269.092	$269.09	$269.10	$269.10
Purchase #5	$146.27	9.296%	$159.8673	$159.87	$159.85	$159.90
Purchase #6	$28.52	10.560%	$31.5317	$31.53	$31.55	$31.50
Purchase #7	$203.88	13.420%	$231.2407	$231.24	$231.25	$231.20
7 purchase totals =	$885.44		$972.8177	$972.82	$972.85	$972.80