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	$9.61	7.338%	$10.3152	$10.32	$10.30	$10.30
Purchase #2	$128.80	11.339%	$143.4046	$143.40	$143.40	$143.40
Purchase #3	$239.63	4.274%	$249.8718	$249.87	$249.85	$249.90
Purchase #4	$104.98	6.253%	$111.5444	$111.54	$111.55	$111.50
Purchase #5	$232.70	5.289%	$245.0075	$245.01	$245.00	$245.00
Purchase #6	$155.95	4.152%	$162.425	$162.43	$162.45	$162.40
Purchase #7	$20.34	12.676%	$22.9183	$22.92	$22.90	$22.90
7 purchase totals =	$892.01		$945.4868	$945.49	$945.45	$945.40