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	$5.89	13.662%	$6.6947	$6.69	$6.70	$6.70
Purchase #2	$156.74	6.557%	$167.0174	$167.02	$167.00	$167.00
Purchase #3	$55.85	5.802%	$59.0904	$59.09	$59.10	$59.10
Purchase #4	$179.74	5.338%	$189.3345	$189.33	$189.35	$189.30
Purchase #5	$152.83	3.220%	$157.7511	$157.75	$157.75	$157.80
Purchase #6	$141.43	10.665%	$156.5135	$156.51	$156.50	$156.50
Purchase #7	$129.73	3.675%	$134.4976	$134.50	$134.50	$134.50
7 purchase totals =	$822.21		$870.8992	$870.89	$870.90	$870.90