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	$35.42	3.308%	$36.5917	$36.59	$36.60	$36.60
Purchase #2	$84.39	5.510%	$89.0399	$89.04	$89.05	$89.00
Purchase #3	$113.38	11.348%	$126.2464	$126.25	$126.25	$126.20
Purchase #4	$162.40	12.123%	$182.0878	$182.09	$182.10	$182.10
Purchase #5	$85.89	5.682%	$90.7703	$90.77	$90.75	$90.80
Purchase #6	$192.60	3.649%	$199.628	$199.63	$199.65	$199.60
Purchase #7	$206.89	3.693%	$214.5304	$214.53	$214.55	$214.50
7 purchase totals =	$880.97		$938.8945	$938.90	$938.95	$938.80