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	$29.86	6.196%	$31.7101	$31.71	$31.70	$31.70
Purchase #2	$128.64	9.585%	$140.9701	$140.97	$140.95	$141.00
Purchase #3	$176.28	11.702%	$196.9083	$196.91	$196.90	$196.90
Purchase #4	$206.93	6.843%	$221.0902	$221.09	$221.10	$221.10
Purchase #5	$196.97	3.202%	$203.277	$203.28	$203.30	$203.30
Purchase #6	$246.32	4.171%	$256.594	$256.59	$256.60	$256.60
Purchase #7	$56.41	9.618%	$61.8355	$61.84	$61.85	$61.80
7 purchase totals =	$1,041.41		$1,112.3852	$1,112.39	$1,112.40	$1,112.40