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	$215.59	12.756%	$243.0907	$243.09	$243.10	$243.10
Purchase #2	$99.43	13.539%	$112.8918	$112.89	$112.90	$112.90
Purchase #3	$151.82	5.366%	$159.9667	$159.97	$159.95	$160.00
Purchase #4	$33.30	3.234%	$34.3769	$34.38	$34.40	$34.40
Purchase #5	$81.37	4.222%	$84.8054	$84.81	$84.80	$84.80
Purchase #6	$135.87	5.145%	$142.8605	$142.86	$142.85	$142.90
Purchase #7	$56.84	7.859%	$61.3071	$61.31	$61.30	$61.30
7 purchase totals =	$774.22		$839.2991	$839.31	$839.30	$839.40