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	$31.45	3.337%	$32.4995	$32.50	$32.50	$32.50
Purchase #2	$42.25	3.519%	$43.7368	$43.74	$43.75	$43.70
Purchase #3	$198.29	12.614%	$223.3023	$223.30	$223.30	$223.30
Purchase #4	$7.97	11.750%	$8.9065	$8.91	$8.90	$8.90
Purchase #5	$136.50	3.647%	$141.4782	$141.48	$141.50	$141.50
Purchase #6	$105.32	9.831%	$115.674	$115.67	$115.65	$115.70
Purchase #7	$19.60	6.129%	$20.8013	$20.80	$20.80	$20.80
7 purchase totals =	$541.38		$586.3986	$586.40	$586.40	$586.40