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	$231.25	12.127%	$259.2937	$259.29	$259.30	$259.30
Purchase #2	$106.28	11.245%	$118.2312	$118.23	$118.25	$118.20
Purchase #3	$37.53	9.321%	$41.0282	$41.03	$41.05	$41.00
Purchase #4	$58.41	8.683%	$63.4817	$63.48	$63.50	$63.50
Purchase #5	$155.92	6.328%	$165.7866	$165.79	$165.80	$165.80
Purchase #6	$240.88	9.704%	$264.255	$264.26	$264.25	$264.30
Purchase #7	$133.54	4.668%	$139.7736	$139.77	$139.75	$139.80
7 purchase totals =	$963.81		$1,051.8500	$1,051.85	$1,051.90	$1,051.90