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	$67.42	5.427%	$71.0789	$71.08	$71.10	$71.10
Purchase #2	$98.66	10.336%	$108.8575	$108.86	$108.85	$108.90
Purchase #3	$220.97	13.840%	$251.5522	$251.55	$251.55	$251.60
Purchase #4	$97.30	10.191%	$107.2158	$107.22	$107.20	$107.20
Purchase #5	$216.90	13.492%	$246.1641	$246.16	$246.15	$246.20
Purchase #6	$103.34	5.649%	$109.1777	$109.18	$109.20	$109.20
Purchase #7	$100.26	8.611%	$108.8934	$108.89	$108.90	$108.90
7 purchase totals =	$904.85		$1,002.9396	$1,002.94	$1,002.95	$1,003.10