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	$57.75	11.301%	$64.2763	$64.28	$64.30	$64.30
Purchase #2	$189.70	3.529%	$196.3945	$196.39	$196.40	$196.40
Purchase #3	$90.77	11.768%	$101.4518	$101.45	$101.45	$101.50
Purchase #4	$15.32	3.307%	$15.8266	$15.83	$15.85	$15.80
Purchase #5	$16.60	12.494%	$18.674	$18.67	$18.65	$18.70
Purchase #6	$150.69	11.371%	$167.825	$167.83	$167.85	$167.80
Purchase #7	$9.70	7.589%	$10.4361	$10.44	$10.45	$10.40
7 purchase totals =	$530.53		$574.8843	$574.89	$574.95	$574.90