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	$31.42	6.815%	$33.5613	$33.56	$33.55	$33.60
Purchase #2	$165.50	10.147%	$182.2933	$182.29	$182.30	$182.30
Purchase #3	$18.75	9.460%	$20.5238	$20.52	$20.50	$20.50
Purchase #4	$81.81	3.248%	$84.4672	$84.47	$84.45	$84.50
Purchase #5	$42.59	3.178%	$43.9435	$43.94	$43.95	$43.90
Purchase #6	$31.80	6.130%	$33.7493	$33.75	$33.75	$33.70
Purchase #7	$124.47	5.459%	$131.2648	$131.26	$131.25	$131.30
7 purchase totals =	$496.34		$529.8032	$529.79	$529.75	$529.80