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	$29.74	8.859%	$32.3747	$32.37	$32.35	$32.40
Purchase #2	$12.73	9.218%	$13.9035	$13.90	$13.90	$13.90
Purchase #3	$6.32	9.109%	$6.8957	$6.90	$6.90	$6.90
Purchase #4	$75.79	10.790%	$83.9677	$83.97	$83.95	$84.00
Purchase #5	$233.74	13.166%	$264.5142	$264.51	$264.50	$264.50
Purchase #6	$56.70	4.171%	$59.065	$59.07	$59.05	$59.10
Purchase #7	$37.97	3.199%	$39.1847	$39.18	$39.20	$39.20
7 purchase totals =	$452.99		$499.9055	$499.90	$499.85	$500.00