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	$115.98	6.474%	$123.4885	$123.49	$123.50	$123.50
Purchase #2	$198.47	6.194%	$210.7632	$210.76	$210.75	$210.80
Purchase #3	$183.98	13.497%	$208.8118	$208.81	$208.80	$208.80
Purchase #4	$116.29	5.816%	$123.0534	$123.05	$123.05	$123.10
Purchase #5	$209.74	10.555%	$231.8781	$231.88	$231.90	$231.90
Purchase #6	$38.82	13.111%	$43.9097	$43.91	$43.90	$43.90
Purchase #7	$123.97	6.140%	$131.5818	$131.58	$131.60	$131.60
7 purchase totals =	$987.25		$1,073.4865	$1,073.48	$1,073.50	$1,073.60