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	$89.62	12.270%	$100.6164	$100.62	$100.60	$100.60
Purchase #2	$132.81	13.731%	$151.0461	$151.05	$151.05	$151.00
Purchase #3	$28.51	3.642%	$29.5483	$29.55	$29.55	$29.50
Purchase #4	$176.52	7.286%	$189.3812	$189.38	$189.40	$189.40
Purchase #5	$118.97	3.663%	$123.3279	$123.33	$123.35	$123.30
Purchase #6	$30.64	7.518%	$32.9435	$32.94	$32.95	$32.90
Purchase #7	$27.56	13.343%	$31.2373	$31.24	$31.25	$31.20
7 purchase totals =	$604.63		$658.1007	$658.11	$658.15	$657.90