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	$80.37	11.857%	$89.8995	$89.90	$89.90	$89.90
Purchase #2	$175.83	10.804%	$194.8267	$194.83	$194.85	$194.80
Purchase #3	$88.39	9.791%	$97.0443	$97.04	$97.05	$97.00
Purchase #4	$131.96	8.233%	$142.8243	$142.82	$142.80	$142.80
Purchase #5	$215.48	8.544%	$233.8906	$233.89	$233.90	$233.90
Purchase #6	$221.27	4.290%	$230.7625	$230.76	$230.75	$230.80
Purchase #7	$234.36	13.505%	$266.0103	$266.01	$266.00	$266.00
7 purchase totals =	$1,147.66		$1,255.2582	$1,255.25	$1,255.25	$1,255.20