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	$54.75	9.380%	$59.8856	$59.89	$59.90	$59.90
Purchase #2	$20.88	11.118%	$23.2014	$23.20	$23.20	$23.20
Purchase #3	$232.48	5.387%	$245.0037	$245.00	$245.00	$245.00
Purchase #4	$208.34	5.460%	$219.7154	$219.72	$219.70	$219.70
Purchase #5	$92.71	8.196%	$100.3085	$100.31	$100.30	$100.30
Purchase #6	$27.75	7.672%	$29.879	$29.88	$29.90	$29.90
Purchase #7	$34.83	7.319%	$37.3792	$37.38	$37.40	$37.40
7 purchase totals =	$671.74		$715.3728	$715.38	$715.40	$715.40