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	$231.85	13.492%	$263.1312	$263.13	$263.15	$263.10
Purchase #2	$170.80	5.128%	$179.5586	$179.56	$179.55	$179.60
Purchase #3	$15.72	7.606%	$16.9157	$16.92	$16.90	$16.90
Purchase #4	$143.74	12.644%	$161.9145	$161.91	$161.90	$161.90
Purchase #5	$127.29	12.224%	$142.8499	$142.85	$142.85	$142.80
Purchase #6	$67.43	6.786%	$72.0058	$72.01	$72.00	$72.00
Purchase #7	$135.76	5.712%	$143.5146	$143.51	$143.50	$143.50
7 purchase totals =	$892.59		$979.8903	$979.89	$979.85	$979.80