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	$38.65	6.324%	$41.0942	$41.09	$41.10	$41.10
Purchase #2	$227.95	11.843%	$254.9461	$254.95	$254.95	$254.90
Purchase #3	$61.95	5.332%	$65.2532	$65.25	$65.25	$65.30
Purchase #4	$172.48	10.600%	$190.7629	$190.76	$190.75	$190.80
Purchase #5	$146.67	11.584%	$163.6603	$163.66	$163.65	$163.70
Purchase #6	$80.74	11.213%	$89.7934	$89.79	$89.80	$89.80
Purchase #7	$192.86	9.566%	$211.309	$211.31	$211.30	$211.30
7 purchase totals =	$921.30		$1,016.8191	$1,016.81	$1,016.80	$1,016.90