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	$69.83	10.234%	$76.9764	$76.98	$77.00	$77.00
Purchase #2	$78.78	8.653%	$85.5968	$85.60	$85.60	$85.60
Purchase #3	$235.46	3.543%	$243.8023	$243.80	$243.80	$243.80
Purchase #4	$110.63	6.866%	$118.2259	$118.23	$118.25	$118.20
Purchase #5	$29.26	11.432%	$32.605	$32.61	$32.60	$32.60
Purchase #6	$137.35	3.811%	$142.5844	$142.58	$142.60	$142.60
Purchase #7	$63.66	13.182%	$72.0517	$72.05	$72.05	$72.10
7 purchase totals =	$724.97		$771.8425	$771.85	$771.90	$771.90