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	$17.97	4.324%	$18.747	$18.75	$18.75	$18.70
Purchase #2	$203.56	8.794%	$221.4611	$221.46	$221.45	$221.50
Purchase #3	$148.53	9.377%	$162.4577	$162.46	$162.45	$162.50
Purchase #4	$188.61	4.188%	$196.509	$196.51	$196.50	$196.50
Purchase #5	$51.40	12.125%	$57.6323	$57.63	$57.65	$57.60
Purchase #6	$117.48	9.567%	$128.7193	$128.72	$128.70	$128.70
Purchase #7	$226.42	8.416%	$245.4755	$245.48	$245.50	$245.50
7 purchase totals =	$953.97		$1,031.0019	$1,031.01	$1,031.00	$1,031.00