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	$97.58	12.285%	$109.5677	$109.57	$109.55	$109.60
Purchase #2	$234.46	9.465%	$256.6516	$256.65	$256.65	$256.70
Purchase #3	$39.69	7.710%	$42.7501	$42.75	$42.75	$42.80
Purchase #4	$90.90	8.217%	$98.3693	$98.37	$98.35	$98.40
Purchase #5	$41.73	10.624%	$46.1634	$46.16	$46.15	$46.20
Purchase #6	$43.41	5.503%	$45.7989	$45.80	$45.80	$45.80
Purchase #7	$27.52	7.743%	$29.6509	$29.65	$29.65	$29.70
7 purchase totals =	$575.29		$628.9519	$628.95	$628.90	$629.20