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	$220.68	9.304%	$241.2121	$241.21	$241.20	$241.20
Purchase #2	$50.58	7.794%	$54.5222	$54.52	$54.50	$54.50
Purchase #3	$82.66	11.674%	$92.3097	$92.31	$92.30	$92.30
Purchase #4	$33.33	11.550%	$37.1796	$37.18	$37.20	$37.20
Purchase #5	$150.87	13.840%	$171.7504	$171.75	$171.75	$171.80
Purchase #6	$124.40	3.416%	$128.6495	$128.65	$128.65	$128.60
Purchase #7	$48.57	13.263%	$55.0118	$55.01	$55.00	$55.00
7 purchase totals =	$711.09		$780.6353	$780.63	$780.60	$780.60