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	$150.29	5.294%	$158.2464	$158.25	$158.25	$158.20
Purchase #2	$204.36	4.285%	$213.1168	$213.12	$213.10	$213.10
Purchase #3	$28.55	11.464%	$31.823	$31.82	$31.80	$31.80
Purchase #4	$138.95	10.498%	$153.537	$153.54	$153.55	$153.50
Purchase #5	$79.78	12.242%	$89.5467	$89.55	$89.55	$89.50
Purchase #6	$79.82	6.286%	$84.8375	$84.84	$84.85	$84.80
Purchase #7	$152.96	10.579%	$169.1416	$169.14	$169.15	$169.10
7 purchase totals =	$834.71		$900.2490	$900.26	$900.25	$900.00