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	$178.84	12.290%	$200.8194	$200.82	$200.80	$200.80
Purchase #2	$72.48	7.687%	$78.0515	$78.05	$78.05	$78.10
Purchase #3	$179.65	5.108%	$188.8265	$188.83	$188.85	$188.80
Purchase #4	$151.75	6.805%	$162.0766	$162.08	$162.10	$162.10
Purchase #5	$169.42	3.648%	$175.6004	$175.60	$175.60	$175.60
Purchase #6	$52.68	11.633%	$58.8083	$58.81	$58.80	$58.80
Purchase #7	$52.48	4.227%	$54.6983	$54.70	$54.70	$54.70
7 purchase totals =	$857.30		$918.8810	$918.89	$918.90	$918.90