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	$13.51	11.339%	$15.0419	$15.04	$15.05	$15.00
Purchase #2	$51.59	6.448%	$54.9165	$54.92	$54.90	$54.90
Purchase #3	$236.99	6.180%	$251.636	$251.64	$251.65	$251.60
Purchase #4	$23.82	7.165%	$25.5267	$25.53	$25.55	$25.50
Purchase #5	$86.91	3.408%	$89.8719	$89.87	$89.85	$89.90
Purchase #6	$29.86	4.725%	$31.2709	$31.27	$31.25	$31.30
Purchase #7	$30.32	13.170%	$34.3131	$34.31	$34.30	$34.30
7 purchase totals =	$473.00		$502.5770	$502.58	$502.55	$502.50