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	$31.79	6.636%	$33.8996	$33.90	$33.90	$33.90
Purchase #2	$58.54	4.358%	$61.0912	$61.09	$61.10	$61.10
Purchase #3	$206.67	8.173%	$223.5611	$223.56	$223.55	$223.60
Purchase #4	$41.54	5.313%	$43.747	$43.75	$43.75	$43.70
Purchase #5	$75.97	8.705%	$82.5832	$82.58	$82.60	$82.60
Purchase #6	$29.78	9.200%	$32.5198	$32.52	$32.50	$32.50
Purchase #7	$101.71	11.303%	$113.2063	$113.21	$113.20	$113.20
7 purchase totals =	$546.00		$590.6082	$590.61	$590.60	$590.60