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	$98.34	7.611%	$105.8247	$105.82	$105.80	$105.80
Purchase #2	$63.79	5.706%	$67.4299	$67.43	$67.45	$67.40
Purchase #3	$204.76	11.686%	$228.6883	$228.69	$228.70	$228.70
Purchase #4	$74.94	11.188%	$83.3243	$83.32	$83.30	$83.30
Purchase #5	$135.37	8.153%	$146.4067	$146.41	$146.40	$146.40
Purchase #6	$114.59	12.483%	$128.8943	$128.89	$128.90	$128.90
Purchase #7	$119.88	8.500%	$130.0698	$130.07	$130.05	$130.10
7 purchase totals =	$811.67		$890.6380	$890.63	$890.60	$890.60