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	$21.80	6.202%	$23.152	$23.15	$23.15	$23.20
Purchase #2	$82.37	10.263%	$90.8236	$90.82	$90.80	$90.80
Purchase #3	$64.80	11.738%	$72.4062	$72.41	$72.40	$72.40
Purchase #4	$195.89	7.566%	$210.711	$210.71	$210.70	$210.70
Purchase #5	$177.44	5.730%	$187.6073	$187.61	$187.60	$187.60
Purchase #6	$65.53	9.692%	$71.8812	$71.88	$71.90	$71.90
Purchase #7	$231.73	9.731%	$254.2796	$254.28	$254.30	$254.30
7 purchase totals =	$839.56		$910.8609	$910.86	$910.85	$910.90