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	$80.85	11.402%	$90.0685	$90.07	$90.05	$90.10
Purchase #2	$10.76	3.118%	$11.0955	$11.10	$11.10	$11.10
Purchase #3	$174.84	6.603%	$186.3847	$186.38	$186.40	$186.40
Purchase #4	$9.56	9.111%	$10.431	$10.43	$10.45	$10.40
Purchase #5	$27.86	6.678%	$29.7205	$29.72	$29.70	$29.70
Purchase #6	$73.72	10.125%	$81.1842	$81.18	$81.20	$81.20
Purchase #7	$38.33	11.648%	$42.7947	$42.79	$42.80	$42.80
7 purchase totals =	$415.92		$451.6791	$451.67	$451.70	$451.70