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	$227.35	12.207%	$255.1026	$255.10	$255.10	$255.10
Purchase #2	$40.40	12.508%	$45.4532	$45.45	$45.45	$45.50
Purchase #3	$123.54	3.759%	$128.1839	$128.18	$128.20	$128.20
Purchase #4	$104.90	9.359%	$114.7176	$114.72	$114.70	$114.70
Purchase #5	$219.54	13.374%	$248.9013	$248.90	$248.90	$248.90
Purchase #6	$37.29	10.587%	$41.2379	$41.24	$41.25	$41.20
Purchase #7	$71.39	7.602%	$76.8171	$76.82	$76.80	$76.80
7 purchase totals =	$824.41		$910.4136	$910.41	$910.40	$910.40