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	$6.66	5.697%	$7.0394	$7.04	$7.05	$7.00
Purchase #2	$72.78	8.458%	$78.9357	$78.94	$78.95	$78.90
Purchase #3	$83.37	4.678%	$87.27	$87.27	$87.25	$87.30
Purchase #4	$150.55	7.114%	$161.2601	$161.26	$161.25	$161.30
Purchase #5	$38.72	10.835%	$42.9153	$42.92	$42.90	$42.90
Purchase #6	$34.78	8.754%	$37.8246	$37.82	$37.80	$37.80
Purchase #7	$39.89	5.364%	$42.0297	$42.03	$42.05	$42.00
7 purchase totals =	$426.75		$457.2748	$457.28	$457.25	$457.20