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	$136.76	13.226%	$154.8479	$154.85	$154.85	$154.80
Purchase #2	$136.85	10.178%	$150.7786	$150.78	$150.80	$150.80
Purchase #3	$74.86	7.592%	$80.5434	$80.54	$80.55	$80.50
Purchase #4	$86.57	9.501%	$94.795	$94.80	$94.80	$94.80
Purchase #5	$210.58	10.564%	$232.8257	$232.83	$232.85	$232.80
Purchase #6	$112.87	5.308%	$118.8611	$118.86	$118.85	$118.90
Purchase #7	$65.62	9.506%	$71.8578	$71.86	$71.85	$71.90
7 purchase totals =	$824.11		$904.5095	$904.52	$904.55	$904.50