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	$80.58	11.808%	$90.0949	$90.09	$90.10	$90.10
Purchase #2	$194.51	4.520%	$203.3019	$203.30	$203.30	$203.30
Purchase #3	$54.35	8.673%	$59.0638	$59.06	$59.05	$59.10
Purchase #4	$56.37	6.234%	$59.8841	$59.88	$59.90	$59.90
Purchase #5	$109.75	10.460%	$121.2299	$121.23	$121.25	$121.20
Purchase #6	$18.83	5.605%	$19.8854	$19.89	$19.90	$19.90
Purchase #7	$92.76	9.226%	$101.318	$101.32	$101.30	$101.30
7 purchase totals =	$607.15		$654.7780	$654.77	$654.80	$654.80