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	$36.75	13.196%	$41.5995	$41.60	$41.60	$41.60
Purchase #2	$120.32	8.687%	$130.7722	$130.77	$130.75	$130.80
Purchase #3	$193.87	7.237%	$207.9004	$207.90	$207.90	$207.90
Purchase #4	$152.48	13.114%	$172.4762	$172.48	$172.50	$172.50
Purchase #5	$86.61	5.693%	$91.5407	$91.54	$91.55	$91.50
Purchase #6	$105.96	4.654%	$110.8914	$110.89	$110.90	$110.90
Purchase #7	$41.87	5.628%	$44.2264	$44.23	$44.25	$44.20
7 purchase totals =	$737.86		$799.4068	$799.41	$799.45	$799.40