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	$33.49	10.123%	$36.8802	$36.88	$36.90	$36.90
Purchase #2	$154.53	6.697%	$164.8789	$164.88	$164.90	$164.90
Purchase #3	$144.43	5.855%	$152.8864	$152.89	$152.90	$152.90
Purchase #4	$217.42	10.542%	$240.3404	$240.34	$240.35	$240.30
Purchase #5	$84.54	12.302%	$94.9401	$94.94	$94.95	$94.90
Purchase #6	$28.53	3.438%	$29.5109	$29.51	$29.50	$29.50
Purchase #7	$13.30	6.173%	$14.121	$14.12	$14.10	$14.10
7 purchase totals =	$676.24		$733.5579	$733.56	$733.60	$733.50