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	$190.48	10.821%	$211.0918	$211.09	$211.10	$211.10
Purchase #2	$52.58	7.112%	$56.3195	$56.32	$56.30	$56.30
Purchase #3	$205.42	9.755%	$225.4587	$225.46	$225.45	$225.50
Purchase #4	$222.78	10.680%	$246.5729	$246.57	$246.55	$246.60
Purchase #5	$39.56	4.807%	$41.4616	$41.46	$41.45	$41.50
Purchase #6	$39.79	12.752%	$44.864	$44.86	$44.85	$44.90
Purchase #7	$40.87	12.384%	$45.9313	$45.93	$45.95	$45.90
7 purchase totals =	$791.48		$871.6998	$871.69	$871.65	$871.80