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	$57.68	3.861%	$59.907	$59.91	$59.90	$59.90
Purchase #2	$232.25	13.614%	$263.8685	$263.87	$263.85	$263.90
Purchase #3	$67.95	6.711%	$72.5101	$72.51	$72.50	$72.50
Purchase #4	$63.97	8.532%	$69.4279	$69.43	$69.45	$69.40
Purchase #5	$73.28	10.825%	$81.2126	$81.21	$81.20	$81.20
Purchase #6	$66.42	10.734%	$73.5495	$73.55	$73.55	$73.50
Purchase #7	$196.82	10.439%	$217.366	$217.37	$217.35	$217.40
7 purchase totals =	$758.37		$837.8416	$837.85	$837.80	$837.80