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	$237.87	6.487%	$253.3006	$253.30	$253.30	$253.30
Purchase #2	$159.65	8.262%	$172.8403	$172.84	$172.85	$172.80
Purchase #3	$248.84	6.803%	$265.7686	$265.77	$265.75	$265.80
Purchase #4	$177.40	6.121%	$188.2587	$188.26	$188.25	$188.30
Purchase #5	$221.37	11.524%	$246.8807	$246.88	$246.90	$246.90
Purchase #6	$184.56	6.500%	$196.5564	$196.56	$196.55	$196.60
Purchase #7	$76.99	7.532%	$82.7889	$82.79	$82.80	$82.80
7 purchase totals =	$1,306.68		$1,406.3942	$1,406.40	$1,406.40	$1,406.50