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	$17.50	6.571%	$18.6499	$18.65	$18.65	$18.60
Purchase #2	$233.90	11.436%	$260.6488	$260.65	$260.65	$260.60
Purchase #3	$213.32	5.732%	$225.5475	$225.55	$225.55	$225.50
Purchase #4	$166.40	7.680%	$179.1795	$179.18	$179.20	$179.20
Purchase #5	$80.54	7.330%	$86.4436	$86.44	$86.45	$86.40
Purchase #6	$172.64	8.832%	$187.8876	$187.89	$187.90	$187.90
Purchase #7	$61.37	4.864%	$64.355	$64.36	$64.35	$64.40
7 purchase totals =	$945.67		$1,022.7119	$1,022.72	$1,022.75	$1,022.60