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	$71.81	9.793%	$78.8424	$78.84	$78.85	$78.80
Purchase #2	$85.49	11.236%	$95.0957	$95.10	$95.10	$95.10
Purchase #3	$95.84	10.523%	$105.9252	$105.93	$105.95	$105.90
Purchase #4	$59.86	10.690%	$66.259	$66.26	$66.25	$66.30
Purchase #5	$135.94	8.474%	$147.4596	$147.46	$147.45	$147.50
Purchase #6	$126.60	11.329%	$140.9425	$140.94	$140.95	$140.90
Purchase #7	$185.38	9.800%	$203.5472	$203.55	$203.55	$203.50
7 purchase totals =	$760.92		$838.0716	$838.08	$838.10	$838.00