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	$29.63	3.153%	$30.5642	$30.56	$30.55	$30.60
Purchase #2	$187.33	4.727%	$196.1851	$196.19	$196.20	$196.20
Purchase #3	$45.43	13.329%	$51.4854	$51.49	$51.50	$51.50
Purchase #4	$174.27	12.401%	$195.8812	$195.88	$195.90	$195.90
Purchase #5	$98.29	11.834%	$109.9216	$109.92	$109.90	$109.90
Purchase #6	$14.52	3.384%	$15.0114	$15.01	$15.00	$15.00
Purchase #7	$135.65	5.150%	$142.636	$142.64	$142.65	$142.60
7 purchase totals =	$685.12		$741.6849	$741.69	$741.70	$741.70