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	$28.60	6.565%	$30.4776	$30.48	$30.50	$30.50
Purchase #2	$72.79	13.502%	$82.6181	$82.62	$82.60	$82.60
Purchase #3	$158.53	13.264%	$179.5574	$179.56	$179.55	$179.60
Purchase #4	$177.99	6.817%	$190.1236	$190.12	$190.10	$190.10
Purchase #5	$205.65	3.829%	$213.5243	$213.52	$213.50	$213.50
Purchase #6	$116.54	12.730%	$131.3755	$131.38	$131.40	$131.40
Purchase #7	$22.42	6.577%	$23.8946	$23.89	$23.90	$23.90
7 purchase totals =	$782.52		$851.5711	$851.57	$851.55	$851.60