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	$160.47	12.610%	$180.7053	$180.71	$180.70	$180.70
Purchase #2	$202.61	3.352%	$209.4015	$209.40	$209.40	$209.40
Purchase #3	$181.67	5.388%	$191.4584	$191.46	$191.45	$191.50
Purchase #4	$220.69	13.650%	$250.8142	$250.81	$250.80	$250.80
Purchase #5	$138.63	6.696%	$147.9127	$147.91	$147.90	$147.90
Purchase #6	$74.54	10.672%	$82.4949	$82.49	$82.50	$82.50
Purchase #7	$139.81	3.588%	$144.8264	$144.83	$144.85	$144.80
7 purchase totals =	$1,118.42		$1,207.6134	$1,207.61	$1,207.60	$1,207.60