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	$92.62	8.537%	$100.527	$100.53	$100.55	$100.50
Purchase #2	$15.30	13.861%	$17.4207	$17.42	$17.40	$17.40
Purchase #3	$156.64	9.535%	$171.5756	$171.58	$171.60	$171.60
Purchase #4	$126.71	8.610%	$137.6197	$137.62	$137.60	$137.60
Purchase #5	$80.75	9.181%	$88.1637	$88.16	$88.15	$88.20
Purchase #6	$208.61	11.373%	$232.3352	$232.34	$232.35	$232.30
Purchase #7	$85.27	6.623%	$90.9174	$90.92	$90.90	$90.90
7 purchase totals =	$765.90		$838.5593	$838.57	$838.55	$838.50