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	$106.75	7.276%	$114.5171	$114.52	$114.50	$114.50
Purchase #2	$90.44	8.840%	$98.4349	$98.43	$98.45	$98.40
Purchase #3	$182.94	4.771%	$191.6681	$191.67	$191.65	$191.70
Purchase #4	$215.46	12.436%	$242.2546	$242.25	$242.25	$242.30
Purchase #5	$8.53	4.221%	$8.8901	$8.89	$8.90	$8.90
Purchase #6	$77.30	11.104%	$85.8834	$85.88	$85.90	$85.90
Purchase #7	$66.55	10.140%	$73.2982	$73.30	$73.30	$73.30
7 purchase totals =	$747.97		$814.9464	$814.94	$814.95	$815.00