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	$34.50	5.160%	$36.2802	$36.28	$36.30	$36.30
Purchase #2	$151.66	11.729%	$169.4482	$169.45	$169.45	$169.40
Purchase #3	$17.61	13.352%	$19.9613	$19.96	$19.95	$20.00
Purchase #4	$78.53	11.443%	$87.5162	$87.52	$87.50	$87.50
Purchase #5	$56.74	4.645%	$59.3756	$59.38	$59.40	$59.40
Purchase #6	$156.67	5.671%	$165.5548	$165.55	$165.55	$165.60
Purchase #7	$243.95	12.383%	$274.1583	$274.16	$274.15	$274.20
7 purchase totals =	$739.66		$812.2946	$812.30	$812.30	$812.40