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	6.752%	$137.5927	$137.59	$137.60	$137.60
Purchase #2	$196.39	12.161%	$220.273	$220.27	$220.25	$220.30
Purchase #3	$236.57	6.302%	$251.4786	$251.48	$251.50	$251.50
Purchase #4	$85.50	12.235%	$95.9609	$95.96	$95.95	$96.00
Purchase #5	$99.37	10.387%	$109.6916	$109.69	$109.70	$109.70
Purchase #6	$103.71	12.727%	$116.9092	$116.91	$116.90	$116.90
Purchase #7	$232.87	10.513%	$257.3516	$257.35	$257.35	$257.40
7 purchase totals =	$1,083.30		$1,189.2576	$1,189.25	$1,189.25	$1,189.40