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	$86.46	11.401%	$96.3173	$96.32	$96.30	$96.30
Purchase #2	$204.64	9.759%	$224.6108	$224.61	$224.60	$224.60
Purchase #3	$48.54	11.199%	$53.976	$53.98	$54.00	$54.00
Purchase #4	$227.98	6.650%	$243.1407	$243.14	$243.15	$243.10
Purchase #5	$126.34	8.588%	$137.1901	$137.19	$137.20	$137.20
Purchase #6	$174.69	5.581%	$184.4394	$184.44	$184.45	$184.40
Purchase #7	$38.30	6.603%	$40.8289	$40.83	$40.85	$40.80
7 purchase totals =	$906.95		$980.5032	$980.51	$980.55	$980.40