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	$212.99	3.859%	$221.2093	$221.21	$221.20	$221.20
Purchase #2	$136.35	7.169%	$146.1249	$146.12	$146.10	$146.10
Purchase #3	$78.96	13.842%	$89.8896	$89.89	$89.90	$89.90
Purchase #4	$59.39	3.795%	$61.6439	$61.64	$61.65	$61.60
Purchase #5	$128.70	3.130%	$132.7283	$132.73	$132.75	$132.70
Purchase #6	$125.75	3.204%	$129.779	$129.78	$129.80	$129.80
Purchase #7	$235.98	12.514%	$265.5105	$265.51	$265.50	$265.50
7 purchase totals =	$978.12		$1,046.8855	$1,046.88	$1,046.90	$1,046.80