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	$158.57	5.519%	$167.3215	$167.32	$167.30	$167.30
Purchase #2	$117.94	11.370%	$131.3498	$131.35	$131.35	$131.30
Purchase #3	$123.84	6.419%	$131.7893	$131.79	$131.80	$131.80
Purchase #4	$249.34	8.679%	$270.9802	$270.98	$271.00	$271.00
Purchase #5	$187.82	9.870%	$206.3578	$206.36	$206.35	$206.40
Purchase #6	$83.48	8.631%	$90.6852	$90.69	$90.70	$90.70
Purchase #7	$5.86	12.850%	$6.613	$6.61	$6.60	$6.60
7 purchase totals =	$926.85		$1,005.0968	$1,005.10	$1,005.10	$1,005.10