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	$137.57	9.802%	$151.0546	$151.05	$151.05	$151.10
Purchase #2	$89.78	3.127%	$92.5874	$92.59	$92.60	$92.60
Purchase #3	$234.31	9.250%	$255.9837	$255.98	$256.00	$256.00
Purchase #4	$245.82	3.584%	$254.6302	$254.63	$254.65	$254.60
Purchase #5	$164.26	13.287%	$186.0852	$186.09	$186.10	$186.10
Purchase #6	$166.29	10.112%	$183.1052	$183.11	$183.10	$183.10
Purchase #7	$190.84	12.680%	$215.0385	$215.04	$215.05	$215.00
7 purchase totals =	$1,228.87		$1,338.4848	$1,338.49	$1,338.55	$1,338.50