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	$27.89	4.572%	$29.1651	$29.17	$29.15	$29.20
Purchase #2	$45.31	13.394%	$51.3788	$51.38	$51.40	$51.40
Purchase #3	$167.97	8.534%	$182.3046	$182.30	$182.30	$182.30
Purchase #4	$157.59	9.257%	$172.1781	$172.18	$172.20	$172.20
Purchase #5	$75.89	12.813%	$85.6138	$85.61	$85.60	$85.60
Purchase #6	$94.85	8.633%	$103.0384	$103.04	$103.05	$103.00
Purchase #7	$136.72	5.787%	$144.632	$144.63	$144.65	$144.60
7 purchase totals =	$706.22		$768.3108	$768.31	$768.35	$768.30