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	$14.77	7.566%	$15.8875	$15.89	$15.90	$15.90
Purchase #2	$208.81	13.338%	$236.6611	$236.66	$236.65	$236.70
Purchase #3	$89.31	6.563%	$95.1714	$95.17	$95.15	$95.20
Purchase #4	$12.48	13.361%	$14.1475	$14.15	$14.15	$14.10
Purchase #5	$90.34	10.119%	$99.4815	$99.48	$99.50	$99.50
Purchase #6	$172.79	12.496%	$194.3818	$194.38	$194.40	$194.40
Purchase #7	$208.96	10.326%	$230.5372	$230.54	$230.55	$230.50
7 purchase totals =	$797.46		$886.2680	$886.27	$886.30	$886.30