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	$11.98	7.534%	$12.8826	$12.88	$12.90	$12.90
Purchase #2	$192.28	12.805%	$216.9015	$216.90	$216.90	$216.90
Purchase #3	$241.52	11.721%	$269.8286	$269.83	$269.85	$269.80
Purchase #4	$231.31	8.454%	$250.8649	$250.86	$250.85	$250.90
Purchase #5	$218.63	3.110%	$225.4294	$225.43	$225.45	$225.40
Purchase #6	$141.38	12.663%	$159.2829	$159.28	$159.30	$159.30
Purchase #7	$31.95	5.663%	$33.7593	$33.76	$33.75	$33.80
7 purchase totals =	$1,069.05		$1,168.9492	$1,168.94	$1,169.00	$1,169.00