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	$159.35	5.645%	$168.3453	$168.35	$168.35	$168.30
Purchase #2	$122.95	6.530%	$130.9786	$130.98	$131.00	$131.00
Purchase #3	$120.86	9.136%	$131.9018	$131.90	$131.90	$131.90
Purchase #4	$128.63	9.830%	$141.2743	$141.27	$141.25	$141.30
Purchase #5	$85.42	8.696%	$92.8481	$92.85	$92.85	$92.80
Purchase #6	$192.49	13.570%	$218.6109	$218.61	$218.60	$218.60
Purchase #7	$161.28	8.838%	$175.5339	$175.53	$175.55	$175.50
7 purchase totals =	$970.98		$1,059.4929	$1,059.49	$1,059.50	$1,059.40