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	$189.44	13.135%	$214.3229	$214.32	$214.30	$214.30
Purchase #2	$112.77	12.664%	$127.0512	$127.05	$127.05	$127.10
Purchase #3	$128.99	11.119%	$143.3324	$143.33	$143.35	$143.30
Purchase #4	$65.39	9.226%	$71.4229	$71.42	$71.40	$71.40
Purchase #5	$222.70	10.368%	$245.7895	$245.79	$245.80	$245.80
Purchase #6	$244.58	11.166%	$271.8898	$271.89	$271.90	$271.90
Purchase #7	$14.78	7.779%	$15.9297	$15.93	$15.95	$15.90
7 purchase totals =	$978.65		$1,089.7384	$1,089.73	$1,089.75	$1,089.70