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	$128.89	12.164%	$144.5682	$144.57	$144.55	$144.60
Purchase #2	$153.94	12.311%	$172.8916	$172.89	$172.90	$172.90
Purchase #3	$119.86	7.419%	$128.7524	$128.75	$128.75	$128.80
Purchase #4	$105.26	7.789%	$113.4587	$113.46	$113.45	$113.50
Purchase #5	$216.89	5.279%	$228.3396	$228.34	$228.35	$228.30
Purchase #6	$189.95	8.775%	$206.6181	$206.62	$206.60	$206.60
Purchase #7	$41.35	5.390%	$43.5788	$43.58	$43.60	$43.60
7 purchase totals =	$956.14		$1,038.2074	$1,038.21	$1,038.20	$1,038.30