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	$249.32	8.549%	$270.6344	$270.63	$270.65	$270.60
Purchase #2	$246.85	5.429%	$260.2515	$260.25	$260.25	$260.30
Purchase #3	$139.83	11.586%	$156.0307	$156.03	$156.05	$156.00
Purchase #4	$206.36	10.220%	$227.45	$227.45	$227.45	$227.50
Purchase #5	$60.29	8.340%	$65.3182	$65.32	$65.30	$65.30
Purchase #6	$40.53	7.869%	$43.7193	$43.72	$43.70	$43.70
Purchase #7	$56.51	9.712%	$61.9983	$62.00	$62.00	$62.00
7 purchase totals =	$999.69		$1,085.4024	$1,085.40	$1,085.40	$1,085.40