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	$135.28	6.309%	$143.8148	$143.81	$143.80	$143.80
Purchase #2	$47.51	8.448%	$51.5236	$51.52	$51.50	$51.50
Purchase #3	$185.72	12.182%	$208.3444	$208.34	$208.35	$208.30
Purchase #4	$71.62	8.279%	$77.5494	$77.55	$77.55	$77.50
Purchase #5	$27.59	13.854%	$31.4123	$31.41	$31.40	$31.40
Purchase #6	$10.58	6.660%	$11.2846	$11.28	$11.30	$11.30
Purchase #7	$82.90	7.259%	$88.9177	$88.92	$88.90	$88.90
7 purchase totals =	$561.20		$612.8468	$612.83	$612.80	$612.70