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	$128.87	4.643%	$134.8534	$134.85	$134.85	$134.90
Purchase #2	$240.83	9.280%	$263.179	$263.18	$263.20	$263.20
Purchase #3	$119.92	9.164%	$130.9095	$130.91	$130.90	$130.90
Purchase #4	$45.90	4.840%	$48.1216	$48.12	$48.10	$48.10
Purchase #5	$69.95	13.465%	$79.3688	$79.37	$79.35	$79.40
Purchase #6	$215.95	7.350%	$231.8223	$231.82	$231.80	$231.80
Purchase #7	$84.94	6.677%	$90.6114	$90.61	$90.60	$90.60
7 purchase totals =	$906.36		$978.8660	$978.86	$978.80	$978.90