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	$168.59	10.196%	$185.7794	$185.78	$185.80	$185.80
Purchase #2	$241.43	11.616%	$269.4745	$269.47	$269.45	$269.50
Purchase #3	$18.94	13.817%	$21.5569	$21.56	$21.55	$21.60
Purchase #4	$124.59	5.584%	$131.5471	$131.55	$131.55	$131.50
Purchase #5	$175.36	4.208%	$182.7391	$182.74	$182.75	$182.70
Purchase #6	$104.67	12.595%	$117.8532	$117.85	$117.85	$117.90
Purchase #7	$36.50	9.529%	$39.9781	$39.98	$40.00	$40.00
7 purchase totals =	$870.08		$948.9283	$948.93	$948.95	$949.00