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	$166.61	7.761%	$179.5406	$179.54	$179.55	$179.50
Purchase #2	$101.95	7.199%	$109.2894	$109.29	$109.30	$109.30
Purchase #3	$223.74	13.268%	$253.4258	$253.43	$253.45	$253.40
Purchase #4	$188.33	13.510%	$213.7734	$213.77	$213.75	$213.80
Purchase #5	$217.60	6.306%	$231.3219	$231.32	$231.30	$231.30
Purchase #6	$39.53	7.759%	$42.5971	$42.60	$42.60	$42.60
Purchase #7	$78.72	8.757%	$85.6135	$85.61	$85.60	$85.60
7 purchase totals =	$1,016.48		$1,115.5617	$1,115.56	$1,115.55	$1,115.50