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	$80.72	3.762%	$83.7567	$83.76	$83.75	$83.80
Purchase #2	$80.73	12.579%	$90.885	$90.89	$90.90	$90.90
Purchase #3	$209.31	9.109%	$228.376	$228.38	$228.40	$228.40
Purchase #4	$224.69	8.149%	$243	$243.00	$243.00	$243.00
Purchase #5	$102.96	8.220%	$111.4233	$111.42	$111.40	$111.40
Purchase #6	$37.76	10.147%	$41.5915	$41.59	$41.60	$41.60
Purchase #7	$191.53	3.871%	$198.9441	$198.94	$198.95	$198.90
7 purchase totals =	$927.70		$997.9766	$997.98	$998.00	$998.00