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	$111.77	4.211%	$116.4766	$116.48	$116.50	$116.50
Purchase #2	$35.74	4.317%	$37.2829	$37.28	$37.30	$37.30
Purchase #3	$94.67	11.401%	$105.4633	$105.46	$105.45	$105.50
Purchase #4	$20.91	4.400%	$21.83	$21.83	$21.85	$21.80
Purchase #5	$56.40	8.690%	$61.3012	$61.30	$61.30	$61.30
Purchase #6	$121.84	9.443%	$133.3454	$133.35	$133.35	$133.30
Purchase #7	$71.79	11.543%	$80.0767	$80.08	$80.10	$80.10
7 purchase totals =	$513.12		$555.7761	$555.78	$555.85	$555.80