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	$135.87	4.352%	$141.7831	$141.78	$141.80	$141.80
Purchase #2	$114.35	11.828%	$127.8753	$127.88	$127.90	$127.90
Purchase #3	$40.27	5.499%	$42.4844	$42.48	$42.50	$42.50
Purchase #4	$159.38	7.814%	$171.834	$171.83	$171.85	$171.80
Purchase #5	$20.61	10.554%	$22.7852	$22.79	$22.80	$22.80
Purchase #6	$46.29	5.233%	$48.7124	$48.71	$48.70	$48.70
Purchase #7	$244.43	12.502%	$274.9886	$274.99	$275.00	$275.00
7 purchase totals =	$761.20		$830.4630	$830.46	$830.55	$830.50