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	$16.85	10.309%	$18.5871	$18.59	$18.60	$18.60
Purchase #2	$58.98	10.240%	$65.0196	$65.02	$65.00	$65.00
Purchase #3	$176.32	7.765%	$190.0112	$190.01	$190.00	$190.00
Purchase #4	$49.53	10.683%	$54.8213	$54.82	$54.80	$54.80
Purchase #5	$81.81	4.360%	$85.3769	$85.38	$85.40	$85.40
Purchase #6	$48.90	4.148%	$50.9284	$50.93	$50.95	$50.90
Purchase #7	$10.37	3.644%	$10.7479	$10.75	$10.75	$10.70
7 purchase totals =	$442.76		$475.4924	$475.50	$475.50	$475.40