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	$99.94	5.257%	$105.1938	$105.19	$105.20	$105.20
Purchase #2	$166.46	7.788%	$179.4239	$179.42	$179.40	$179.40
Purchase #3	$228.30	5.402%	$240.6328	$240.63	$240.65	$240.60
Purchase #4	$64.88	4.491%	$67.7938	$67.79	$67.80	$67.80
Purchase #5	$133.45	12.552%	$150.2006	$150.20	$150.20	$150.20
Purchase #6	$91.62	5.216%	$96.3989	$96.40	$96.40	$96.40
Purchase #7	$138.95	8.380%	$150.594	$150.59	$150.60	$150.60
7 purchase totals =	$923.60		$990.2378	$990.22	$990.25	$990.20