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	$203.52	6.371%	$216.4863	$216.49	$216.50	$216.50
Purchase #2	$134.63	5.110%	$141.5096	$141.51	$141.50	$141.50
Purchase #3	$166.49	12.436%	$187.1947	$187.19	$187.20	$187.20
Purchase #4	$36.37	5.585%	$38.4013	$38.40	$38.40	$38.40
Purchase #5	$244.71	11.382%	$272.5629	$272.56	$272.55	$272.60
Purchase #6	$85.62	6.166%	$90.8993	$90.90	$90.90	$90.90
Purchase #7	$196.71	6.661%	$209.8129	$209.81	$209.80	$209.80
7 purchase totals =	$1,068.05		$1,156.8670	$1,156.86	$1,156.85	$1,156.90