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	$189.99	12.794%	$214.2973	$214.30	$214.30	$214.30
Purchase #2	$10.95	12.868%	$12.359	$12.36	$12.35	$12.40
Purchase #3	$164.43	4.636%	$172.053	$172.05	$172.05	$172.10
Purchase #4	$29.89	4.785%	$31.3202	$31.32	$31.30	$31.30
Purchase #5	$92.56	7.339%	$99.353	$99.35	$99.35	$99.40
Purchase #6	$172.35	9.540%	$188.7922	$188.79	$188.80	$188.80
Purchase #7	$98.47	10.477%	$108.7867	$108.79	$108.80	$108.80
7 purchase totals =	$758.64		$826.9614	$826.96	$826.95	$827.10