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	$57.65	3.172%	$59.4787	$59.48	$59.50	$59.50
Purchase #2	$112.80	3.419%	$116.6566	$116.66	$116.65	$116.70
Purchase #3	$163.76	12.676%	$184.5182	$184.52	$184.50	$184.50
Purchase #4	$64.82	4.559%	$67.7751	$67.78	$67.80	$67.80
Purchase #5	$204.32	8.201%	$221.0763	$221.08	$221.10	$221.10
Purchase #6	$36.41	3.727%	$37.767	$37.77	$37.75	$37.80
Purchase #7	$101.45	4.645%	$106.1624	$106.16	$106.15	$106.20
7 purchase totals =	$741.21		$793.4343	$793.45	$793.45	$793.60