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	$90.75	8.646%	$98.5962	$98.60	$98.60	$98.60
Purchase #2	$146.98	13.297%	$166.5239	$166.52	$166.50	$166.50
Purchase #3	$37.50	12.358%	$42.1343	$42.13	$42.15	$42.10
Purchase #4	$148.66	12.840%	$167.7479	$167.75	$167.75	$167.70
Purchase #5	$39.64	8.747%	$43.1073	$43.11	$43.10	$43.10
Purchase #6	$215.47	5.273%	$226.8317	$226.83	$226.85	$226.80
Purchase #7	$205.62	7.704%	$221.461	$221.46	$221.45	$221.50
7 purchase totals =	$884.62		$966.4023	$966.40	$966.40	$966.30