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	$120.76	12.367%	$135.6944	$135.69	$135.70	$135.70
Purchase #2	$46.46	9.107%	$50.6911	$50.69	$50.70	$50.70
Purchase #3	$90.47	8.839%	$98.4666	$98.47	$98.45	$98.50
Purchase #4	$190.62	9.558%	$208.8395	$208.84	$208.85	$208.80
Purchase #5	$167.91	10.296%	$185.198	$185.20	$185.20	$185.20
Purchase #6	$52.25	13.267%	$59.182	$59.18	$59.20	$59.20
Purchase #7	$20.41	4.403%	$21.3087	$21.31	$21.30	$21.30
7 purchase totals =	$688.88		$759.3803	$759.38	$759.40	$759.40