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	$99.27	6.664%	$105.8854	$105.89	$105.90	$105.90
Purchase #2	$65.28	3.849%	$67.7926	$67.79	$67.80	$67.80
Purchase #3	$200.63	3.108%	$206.8656	$206.87	$206.85	$206.90
Purchase #4	$62.90	13.626%	$71.4708	$71.47	$71.45	$71.50
Purchase #5	$188.46	4.288%	$196.5412	$196.54	$196.55	$196.50
Purchase #6	$27.45	13.694%	$31.209	$31.21	$31.20	$31.20
Purchase #7	$107.33	13.318%	$121.6242	$121.62	$121.60	$121.60
7 purchase totals =	$751.32		$801.3888	$801.39	$801.35	$801.40