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	$162.82	10.740%	$180.3069	$180.31	$180.30	$180.30
Purchase #2	$63.76	3.609%	$66.0611	$66.06	$66.05	$66.10
Purchase #3	$201.57	13.189%	$228.1551	$228.16	$228.15	$228.20
Purchase #4	$151.52	12.549%	$170.5342	$170.53	$170.55	$170.50
Purchase #5	$242.49	9.799%	$266.2516	$266.25	$266.25	$266.30
Purchase #6	$27.81	3.313%	$28.7313	$28.73	$28.75	$28.70
Purchase #7	$95.83	5.148%	$100.7633	$100.76	$100.75	$100.80
7 purchase totals =	$945.80		$1,040.8035	$1,040.80	$1,040.80	$1,040.90