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	$78.58	3.173%	$81.0733	$81.07	$81.05	$81.10
Purchase #2	$77.56	7.246%	$83.18	$83.18	$83.20	$83.20
Purchase #3	$38.73	8.528%	$42.0329	$42.03	$42.05	$42.00
Purchase #4	$18.27	13.361%	$20.7111	$20.71	$20.70	$20.70
Purchase #5	$212.61	13.525%	$241.3655	$241.37	$241.35	$241.40
Purchase #6	$78.96	12.854%	$89.1095	$89.11	$89.10	$89.10
Purchase #7	$142.91	11.331%	$159.1031	$159.10	$159.10	$159.10
7 purchase totals =	$647.62		$716.5754	$716.57	$716.55	$716.60