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	$203.77	13.410%	$231.0956	$231.10	$231.10	$231.10
Purchase #2	$72.49	7.677%	$78.0551	$78.06	$78.05	$78.10
Purchase #3	$91.52	12.450%	$102.9142	$102.91	$102.90	$102.90
Purchase #4	$29.25	9.467%	$32.0191	$32.02	$32.00	$32.00
Purchase #5	$91.97	11.316%	$102.3773	$102.38	$102.40	$102.40
Purchase #6	$88.83	4.515%	$92.8407	$92.84	$92.85	$92.80
Purchase #7	$123.74	13.840%	$140.8656	$140.87	$140.85	$140.90
7 purchase totals =	$701.57		$780.1676	$780.18	$780.15	$780.20