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	$191.54	9.369%	$209.4854	$209.49	$209.50	$209.50
Purchase #2	$37.88	8.283%	$41.0176	$41.02	$41.00	$41.00
Purchase #3	$32.36	3.558%	$33.5114	$33.51	$33.50	$33.50
Purchase #4	$227.75	10.492%	$251.6455	$251.65	$251.65	$251.60
Purchase #5	$37.72	6.872%	$40.3121	$40.31	$40.30	$40.30
Purchase #6	$181.43	13.829%	$206.52	$206.52	$206.50	$206.50
Purchase #7	$44.96	7.453%	$48.3109	$48.31	$48.30	$48.30
7 purchase totals =	$753.64		$830.8029	$830.81	$830.75	$830.70