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	$73.97	8.819%	$80.4934	$80.49	$80.50	$80.50
Purchase #2	$245.95	11.766%	$274.8885	$274.89	$274.90	$274.90
Purchase #3	$194.35	8.838%	$211.5267	$211.53	$211.55	$211.50
Purchase #4	$8.98	11.407%	$10.0043	$10.00	$10.00	$10.00
Purchase #5	$166.75	9.481%	$182.5596	$182.56	$182.55	$182.60
Purchase #6	$124.40	10.789%	$137.8215	$137.82	$137.80	$137.80
Purchase #7	$186.77	6.779%	$199.4311	$199.43	$199.45	$199.40
7 purchase totals =	$1,001.17		$1,096.7251	$1,096.72	$1,096.75	$1,096.70