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	$57.29	12.671%	$64.5492	$64.55	$64.55	$64.50
Purchase #2	$227.93	4.841%	$238.9641	$238.96	$238.95	$239.00
Purchase #3	$199.36	12.551%	$224.3817	$224.38	$224.40	$224.40
Purchase #4	$125.80	8.814%	$136.888	$136.89	$136.90	$136.90
Purchase #5	$236.85	11.227%	$263.4411	$263.44	$263.45	$263.40
Purchase #6	$83.59	8.569%	$90.7528	$90.75	$90.75	$90.80
Purchase #7	$86.33	9.866%	$94.8473	$94.85	$94.85	$94.80
7 purchase totals =	$1,017.15		$1,113.8242	$1,113.82	$1,113.85	$1,113.80