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	$115.83	6.217%	$123.0312	$123.03	$123.05	$123.00
Purchase #2	$240.74	9.439%	$263.4634	$263.46	$263.45	$263.50
Purchase #3	$151.62	11.743%	$169.4247	$169.42	$169.40	$169.40
Purchase #4	$179.28	9.348%	$196.0391	$196.04	$196.05	$196.00
Purchase #5	$47.58	4.467%	$49.7054	$49.71	$49.70	$49.70
Purchase #6	$145.34	3.357%	$150.2191	$150.22	$150.20	$150.20
Purchase #7	$44.58	6.781%	$47.603	$47.60	$47.60	$47.60
7 purchase totals =	$924.97		$999.4859	$999.48	$999.45	$999.40