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	$131.76	4.381%	$137.5324	$137.53	$137.55	$137.50
Purchase #2	$222.30	12.710%	$250.5543	$250.55	$250.55	$250.60
Purchase #3	$26.44	11.795%	$29.5586	$29.56	$29.55	$29.60
Purchase #4	$180.96	3.739%	$187.7261	$187.73	$187.75	$187.70
Purchase #5	$71.78	7.103%	$76.8785	$76.88	$76.90	$76.90
Purchase #6	$235.56	13.592%	$267.5773	$267.58	$267.60	$267.60
Purchase #7	$135.78	5.492%	$143.237	$143.24	$143.25	$143.20
7 purchase totals =	$1,004.58		$1,093.0642	$1,093.07	$1,093.15	$1,093.10