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	$75.89	3.150%	$78.2805	$78.28	$78.30	$78.30
Purchase #2	$95.26	9.860%	$104.6526	$104.65	$104.65	$104.70
Purchase #3	$248.27	12.380%	$279.0058	$279.01	$279.00	$279.00
Purchase #4	$215.66	12.779%	$243.2192	$243.22	$243.20	$243.20
Purchase #5	$212.60	7.666%	$228.8979	$228.90	$228.90	$228.90
Purchase #6	$45.64	12.237%	$51.225	$51.23	$51.25	$51.20
Purchase #7	$41.25	11.578%	$46.0259	$46.03	$46.05	$46.00
7 purchase totals =	$934.57		$1,031.3069	$1,031.32	$1,031.35	$1,031.30