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	$73.30	7.119%	$78.5182	$78.52	$78.50	$78.50
Purchase #2	$50.56	6.239%	$53.7144	$53.71	$53.70	$53.70
Purchase #3	$73.49	6.246%	$78.0802	$78.08	$78.10	$78.10
Purchase #4	$102.72	13.776%	$116.8707	$116.87	$116.85	$116.90
Purchase #5	$25.57	11.192%	$28.4318	$28.43	$28.45	$28.40
Purchase #6	$18.84	8.414%	$20.4252	$20.43	$20.45	$20.40
Purchase #7	$106.43	13.110%	$120.383	$120.38	$120.40	$120.40
7 purchase totals =	$450.91		$496.4235	$496.42	$496.45	$496.40