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	$38.84	13.854%	$44.2209	$44.22	$44.20	$44.20
Purchase #2	$234.66	10.478%	$259.2477	$259.25	$259.25	$259.20
Purchase #3	$42.30	9.504%	$46.3202	$46.32	$46.30	$46.30
Purchase #4	$198.74	8.204%	$215.0446	$215.04	$215.05	$215.00
Purchase #5	$125.28	13.656%	$142.3882	$142.39	$142.40	$142.40
Purchase #6	$243.83	7.661%	$262.5098	$262.51	$262.50	$262.50
Purchase #7	$119.30	9.293%	$130.3865	$130.39	$130.40	$130.40
7 purchase totals =	$1,002.95		$1,100.1179	$1,100.12	$1,100.10	$1,100.00