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	$125.90	11.567%	$140.4629	$140.46	$140.45	$140.50
Purchase #2	$179.64	11.675%	$200.613	$200.61	$200.60	$200.60
Purchase #3	$24.37	11.724%	$27.2271	$27.23	$27.25	$27.20
Purchase #4	$56.48	5.860%	$59.7897	$59.79	$59.80	$59.80
Purchase #5	$63.48	9.425%	$69.463	$69.46	$69.45	$69.50
Purchase #6	$160.89	8.550%	$174.6461	$174.65	$174.65	$174.60
Purchase #7	$91.76	11.166%	$102.0059	$102.01	$102.00	$102.00
7 purchase totals =	$702.52		$774.2077	$774.21	$774.20	$774.20