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	$19.91	4.732%	$20.8521	$20.85	$20.85	$20.90
Purchase #2	$162.83	5.280%	$171.4274	$171.43	$171.45	$171.40
Purchase #3	$44.66	5.601%	$47.1614	$47.16	$47.15	$47.20
Purchase #4	$197.81	9.756%	$217.1083	$217.11	$217.10	$217.10
Purchase #5	$231.78	12.223%	$260.1105	$260.11	$260.10	$260.10
Purchase #6	$177.96	3.858%	$184.8257	$184.83	$184.85	$184.80
Purchase #7	$158.43	4.319%	$165.2726	$165.27	$165.25	$165.30
7 purchase totals =	$993.38		$1,066.7580	$1,066.76	$1,066.75	$1,066.80