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	$55.72	6.321%	$59.2421	$59.24	$59.25	$59.20
Purchase #2	$5.87	11.243%	$6.53	$6.53	$6.55	$6.50
Purchase #3	$142.61	12.571%	$160.5375	$160.54	$160.55	$160.50
Purchase #4	$173.54	6.105%	$184.1346	$184.13	$184.15	$184.10
Purchase #5	$245.62	4.145%	$255.8009	$255.80	$255.80	$255.80
Purchase #6	$34.81	8.216%	$37.67	$37.67	$37.65	$37.70
Purchase #7	$100.49	9.287%	$109.8225	$109.82	$109.80	$109.80
7 purchase totals =	$758.66		$813.7376	$813.73	$813.75	$813.60