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	$48.30	7.660%	$51.9998	$52.00	$52.00	$52.00
Purchase #2	$208.61	4.785%	$218.592	$218.59	$218.60	$218.60
Purchase #3	$136.77	11.808%	$152.9198	$152.92	$152.90	$152.90
Purchase #4	$31.87	3.729%	$33.0584	$33.06	$33.05	$33.10
Purchase #5	$140.51	7.308%	$150.7785	$150.78	$150.80	$150.80
Purchase #6	$151.51	12.145%	$169.9109	$169.91	$169.90	$169.90
Purchase #7	$40.97	11.569%	$45.7098	$45.71	$45.70	$45.70
7 purchase totals =	$758.54		$822.9692	$822.97	$822.95	$823.00