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	$183.31	11.737%	$204.8251	$204.83	$204.85	$204.80
Purchase #2	$249.66	11.434%	$278.2061	$278.21	$278.20	$278.20
Purchase #3	$40.27	5.668%	$42.5525	$42.55	$42.55	$42.60
Purchase #4	$22.43	12.124%	$25.1494	$25.15	$25.15	$25.10
Purchase #5	$57.89	9.765%	$63.543	$63.54	$63.55	$63.50
Purchase #6	$38.78	3.183%	$40.0144	$40.01	$40.00	$40.00
Purchase #7	$235.71	4.165%	$245.5273	$245.53	$245.55	$245.50
7 purchase totals =	$828.05		$899.8178	$899.82	$899.85	$899.70