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	$35.52	6.687%	$37.8952	$37.90	$37.90	$37.90
Purchase #2	$100.35	11.491%	$111.8812	$111.88	$111.90	$111.90
Purchase #3	$35.37	10.156%	$38.9622	$38.96	$38.95	$39.00
Purchase #4	$88.63	13.470%	$100.5685	$100.57	$100.55	$100.60
Purchase #5	$20.76	3.260%	$21.4368	$21.44	$21.45	$21.40
Purchase #6	$211.36	7.751%	$227.7425	$227.74	$227.75	$227.70
Purchase #7	$239.65	12.311%	$269.1533	$269.15	$269.15	$269.20
7 purchase totals =	$731.64		$807.6397	$807.64	$807.65	$807.70