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	$11.86	3.291%	$12.2503	$12.25	$12.25	$12.30
Purchase #2	$117.41	4.549%	$122.751	$122.75	$122.75	$122.80
Purchase #3	$174.80	5.771%	$184.8877	$184.89	$184.90	$184.90
Purchase #4	$172.65	13.787%	$196.4533	$196.45	$196.45	$196.50
Purchase #5	$244.36	12.207%	$274.189	$274.19	$274.20	$274.20
Purchase #6	$47.98	13.167%	$54.2975	$54.30	$54.30	$54.30
Purchase #7	$68.89	7.254%	$73.8873	$73.89	$73.90	$73.90
7 purchase totals =	$837.95		$918.7161	$918.72	$918.75	$918.90