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	$6.44	3.252%	$6.6494	$6.65	$6.65	$6.60
Purchase #2	$54.88	8.641%	$59.6222	$59.62	$59.60	$59.60
Purchase #3	$221.33	10.553%	$244.687	$244.69	$244.70	$244.70
Purchase #4	$174.33	12.581%	$196.2625	$196.26	$196.25	$196.30
Purchase #5	$125.83	8.715%	$136.7961	$136.80	$136.80	$136.80
Purchase #6	$125.84	9.566%	$137.8779	$137.88	$137.90	$137.90
Purchase #7	$214.62	3.834%	$222.8485	$222.85	$222.85	$222.80
7 purchase totals =	$923.27		$1,004.7436	$1,004.75	$1,004.75	$1,004.70