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	$136.32	9.684%	$149.5212	$149.52	$149.50	$149.50
Purchase #2	$33.54	5.561%	$35.4052	$35.41	$35.40	$35.40
Purchase #3	$137.35	11.693%	$153.4103	$153.41	$153.40	$153.40
Purchase #4	$119.62	7.349%	$128.4109	$128.41	$128.40	$128.40
Purchase #5	$76.53	12.139%	$85.82	$85.82	$85.80	$85.80
Purchase #6	$124.73	12.452%	$140.2614	$140.26	$140.25	$140.30
Purchase #7	$60.37	11.505%	$67.3156	$67.32	$67.30	$67.30
7 purchase totals =	$688.46		$760.1446	$760.15	$760.05	$760.10