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	$55.70	7.515%	$59.8859	$59.89	$59.90	$59.90
Purchase #2	$82.64	9.766%	$90.7106	$90.71	$90.70	$90.70
Purchase #3	$189.28	8.256%	$204.907	$204.91	$204.90	$204.90
Purchase #4	$68.99	11.567%	$76.9701	$76.97	$76.95	$77.00
Purchase #5	$246.56	13.452%	$279.7273	$279.73	$279.75	$279.70
Purchase #6	$71.95	8.415%	$78.0046	$78.00	$78.00	$78.00
Purchase #7	$196.69	11.230%	$218.7783	$218.78	$218.80	$218.80
7 purchase totals =	$911.81		$1,008.9838	$1,008.99	$1,009.00	$1,009.00