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	$57.71	6.423%	$61.4167	$61.42	$61.40	$61.40
Purchase #2	$219.63	13.744%	$249.8159	$249.82	$249.80	$249.80
Purchase #3	$136.90	7.297%	$146.8896	$146.89	$146.90	$146.90
Purchase #4	$244.33	11.265%	$271.8538	$271.85	$271.85	$271.90
Purchase #5	$196.83	6.536%	$209.6948	$209.69	$209.70	$209.70
Purchase #6	$119.90	11.176%	$133.3	$133.30	$133.30	$133.30
Purchase #7	$71.95	9.260%	$78.6126	$78.61	$78.60	$78.60
7 purchase totals =	$1,047.25		$1,151.5834	$1,151.58	$1,151.55	$1,151.60