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	$131.38	11.848%	$146.9459	$146.95	$146.95	$146.90
Purchase #2	$127.89	4.134%	$133.177	$133.18	$133.20	$133.20
Purchase #3	$247.59	3.785%	$256.9613	$256.96	$256.95	$257.00
Purchase #4	$226.41	5.489%	$238.8376	$238.84	$238.85	$238.80
Purchase #5	$166.74	13.851%	$189.8352	$189.84	$189.85	$189.80
Purchase #6	$185.43	7.239%	$198.8533	$198.85	$198.85	$198.90
Purchase #7	$218.30	3.193%	$225.2703	$225.27	$225.25	$225.30
7 purchase totals =	$1,303.74		$1,389.8806	$1,389.89	$1,389.90	$1,389.90