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	$54.55	8.447%	$59.1578	$59.16	$59.15	$59.20
Purchase #2	$152.80	10.362%	$168.6331	$168.63	$168.65	$168.60
Purchase #3	$96.97	3.465%	$100.33	$100.33	$100.35	$100.30
Purchase #4	$136.94	11.391%	$152.5388	$152.54	$152.55	$152.50
Purchase #5	$121.51	8.827%	$132.2357	$132.24	$132.25	$132.20
Purchase #6	$41.71	11.196%	$46.3799	$46.38	$46.40	$46.40
Purchase #7	$36.58	12.594%	$41.1869	$41.19	$41.20	$41.20
7 purchase totals =	$641.06		$700.4622	$700.47	$700.55	$700.40