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	$34.77	6.382%	$36.989	$36.99	$37.00	$37.00
Purchase #2	$234.70	13.232%	$265.7555	$265.76	$265.75	$265.80
Purchase #3	$64.78	11.779%	$72.4104	$72.41	$72.40	$72.40
Purchase #4	$127.99	11.238%	$142.3735	$142.37	$142.35	$142.40
Purchase #5	$170.39	10.161%	$187.7033	$187.70	$187.70	$187.70
Purchase #6	$45.89	13.220%	$51.9567	$51.96	$51.95	$52.00
Purchase #7	$27.57	13.287%	$31.2332	$31.23	$31.25	$31.20
7 purchase totals =	$706.09		$788.4216	$788.42	$788.40	$788.50