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	$75.60	3.394%	$78.1659	$78.17	$78.15	$78.20
Purchase #2	$179.72	6.415%	$191.249	$191.25	$191.25	$191.20
Purchase #3	$39.46	7.552%	$42.44	$42.44	$42.45	$42.40
Purchase #4	$159.53	12.447%	$179.3867	$179.39	$179.40	$179.40
Purchase #5	$212.38	11.741%	$237.3155	$237.32	$237.30	$237.30
Purchase #6	$173.43	8.587%	$188.3224	$188.32	$188.30	$188.30
Purchase #7	$76.44	6.455%	$81.3742	$81.37	$81.35	$81.40
7 purchase totals =	$916.56		$998.2537	$998.26	$998.20	$998.20