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	$171.38	3.492%	$177.3646	$177.36	$177.35	$177.40
Purchase #2	$94.38	9.762%	$103.5934	$103.59	$103.60	$103.60
Purchase #3	$139.59	7.339%	$149.8345	$149.83	$149.85	$149.80
Purchase #4	$62.54	13.591%	$71.0398	$71.04	$71.05	$71.00
Purchase #5	$210.60	7.323%	$226.0222	$226.02	$226.00	$226.00
Purchase #6	$81.81	11.154%	$90.9351	$90.94	$90.95	$90.90
Purchase #7	$94.48	9.121%	$103.0975	$103.10	$103.10	$103.10
7 purchase totals =	$854.78		$921.8871	$921.88	$921.90	$921.80