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	$23.25	11.386%	$25.8972	$25.90	$25.90	$25.90
Purchase #2	$207.73	3.692%	$215.3994	$215.40	$215.40	$215.40
Purchase #3	$210.64	12.220%	$236.3802	$236.38	$236.40	$236.40
Purchase #4	$27.44	4.711%	$28.7327	$28.73	$28.75	$28.70
Purchase #5	$56.28	5.734%	$59.5071	$59.51	$59.50	$59.50
Purchase #6	$57.63	3.831%	$59.8378	$59.84	$59.85	$59.80
Purchase #7	$10.25	11.148%	$11.3927	$11.39	$11.40	$11.40
7 purchase totals =	$593.22		$637.1471	$637.15	$637.20	$637.10