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	$243.98	4.549%	$255.0787	$255.08	$255.10	$255.10
Purchase #2	$216.51	10.742%	$239.7675	$239.77	$239.75	$239.80
Purchase #3	$186.35	5.305%	$196.2359	$196.24	$196.25	$196.20
Purchase #4	$131.58	8.599%	$142.8946	$142.89	$142.90	$142.90
Purchase #5	$82.48	6.696%	$88.0029	$88.00	$88.00	$88.00
Purchase #6	$40.25	13.456%	$45.666	$45.67	$45.65	$45.70
Purchase #7	$184.79	13.421%	$209.5907	$209.59	$209.60	$209.60
7 purchase totals =	$1,085.94		$1,177.2363	$1,177.24	$1,177.25	$1,177.30