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	$26.54	3.427%	$27.4495	$27.45	$27.45	$27.40
Purchase #2	$61.27	6.555%	$65.2862	$65.29	$65.30	$65.30
Purchase #3	$78.54	8.765%	$85.424	$85.42	$85.40	$85.40
Purchase #4	$59.62	13.586%	$67.72	$67.72	$67.70	$67.70
Purchase #5	$171.69	12.132%	$192.5194	$192.52	$192.50	$192.50
Purchase #6	$47.42	12.232%	$53.2204	$53.22	$53.20	$53.20
Purchase #7	$121.99	13.813%	$138.8405	$138.84	$138.85	$138.80
7 purchase totals =	$567.07		$630.4600	$630.46	$630.40	$630.30