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	$85.62	6.234%	$90.9576	$90.96	$90.95	$91.00
Purchase #2	$35.43	7.486%	$38.0823	$38.08	$38.10	$38.10
Purchase #3	$65.48	10.609%	$72.4268	$72.43	$72.45	$72.40
Purchase #4	$61.90	3.665%	$64.1686	$64.17	$64.15	$64.20
Purchase #5	$125.60	13.143%	$142.1076	$142.11	$142.10	$142.10
Purchase #6	$19.83	5.765%	$20.9732	$20.97	$20.95	$21.00
Purchase #7	$236.69	6.798%	$252.7802	$252.78	$252.80	$252.80
7 purchase totals =	$630.55		$681.4963	$681.50	$681.50	$681.60