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	$123.32	4.317%	$128.6437	$128.64	$128.65	$128.60
Purchase #2	$228.89	5.215%	$240.8266	$240.83	$240.85	$240.80
Purchase #3	$94.48	8.163%	$102.1924	$102.19	$102.20	$102.20
Purchase #4	$76.62	6.526%	$81.6202	$81.62	$81.60	$81.60
Purchase #5	$49.95	6.641%	$53.2672	$53.27	$53.25	$53.30
Purchase #6	$68.63	4.436%	$71.6744	$71.67	$71.65	$71.70
Purchase #7	$31.83	7.828%	$34.3217	$34.32	$34.30	$34.30
7 purchase totals =	$673.72		$712.5462	$712.54	$712.50	$712.50