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	$79.60	12.557%	$89.5954	$89.60	$89.60	$89.60
Purchase #2	$171.91	11.371%	$191.4579	$191.46	$191.45	$191.50
Purchase #3	$75.69	12.603%	$85.2292	$85.23	$85.25	$85.20
Purchase #4	$33.77	3.611%	$34.9894	$34.99	$35.00	$35.00
Purchase #5	$46.38	9.423%	$50.7504	$50.75	$50.75	$50.80
Purchase #6	$201.81	10.273%	$222.5419	$222.54	$222.55	$222.50
Purchase #7	$131.34	5.849%	$139.0221	$139.02	$139.00	$139.00
7 purchase totals =	$740.50		$813.5863	$813.59	$813.60	$813.60