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	$240.34	12.519%	$270.4282	$270.43	$270.45	$270.40
Purchase #2	$67.79	13.380%	$76.8603	$76.86	$76.85	$76.90
Purchase #3	$37.40	5.256%	$39.3657	$39.37	$39.35	$39.40
Purchase #4	$242.72	13.226%	$274.8221	$274.82	$274.80	$274.80
Purchase #5	$86.67	12.832%	$97.7915	$97.79	$97.80	$97.80
Purchase #6	$129.31	8.472%	$140.2651	$140.27	$140.25	$140.30
Purchase #7	$74.43	5.192%	$78.2944	$78.29	$78.30	$78.30
7 purchase totals =	$878.66		$977.8273	$977.83	$977.80	$977.90