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	$192.65	12.269%	$216.2862	$216.29	$216.30	$216.30
Purchase #2	$81.84	4.272%	$85.3362	$85.34	$85.35	$85.30
Purchase #3	$53.76	11.527%	$59.9569	$59.96	$59.95	$60.00
Purchase #4	$41.53	7.414%	$44.609	$44.61	$44.60	$44.60
Purchase #5	$222.91	8.268%	$241.3402	$241.34	$241.35	$241.30
Purchase #6	$33.81	10.786%	$37.4567	$37.46	$37.45	$37.50
Purchase #7	$26.88	6.628%	$28.6616	$28.66	$28.65	$28.70
7 purchase totals =	$653.38		$713.6468	$713.66	$713.65	$713.70