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	$95.89	4.602%	$100.3029	$100.30	$100.30	$100.30
Purchase #2	$190.66	13.206%	$215.8386	$215.84	$215.85	$215.80
Purchase #3	$136.64	3.629%	$141.5987	$141.60	$141.60	$141.60
Purchase #4	$69.55	3.466%	$71.9606	$71.96	$71.95	$72.00
Purchase #5	$68.46	7.350%	$73.4918	$73.49	$73.50	$73.50
Purchase #6	$99.60	6.264%	$105.8389	$105.84	$105.85	$105.80
Purchase #7	$170.68	13.227%	$193.2558	$193.26	$193.25	$193.30
7 purchase totals =	$831.48		$902.2873	$902.29	$902.30	$902.30