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	$54.68	9.735%	$60.0031	$60.00	$60.00	$60.00
Purchase #2	$29.99	11.566%	$33.4586	$33.46	$33.45	$33.50
Purchase #3	$39.78	9.871%	$43.7067	$43.71	$43.70	$43.70
Purchase #4	$140.50	11.246%	$156.3006	$156.30	$156.30	$156.30
Purchase #5	$167.27	11.132%	$185.8905	$185.89	$185.90	$185.90
Purchase #6	$128.97	8.330%	$139.7132	$139.71	$139.70	$139.70
Purchase #7	$185.39	7.213%	$198.7622	$198.76	$198.75	$198.80
7 purchase totals =	$746.58		$817.8349	$817.83	$817.80	$817.90