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	$53.62	5.188%	$56.4018	$56.40	$56.40	$56.40
Purchase #2	$85.26	5.484%	$89.9357	$89.94	$89.95	$89.90
Purchase #3	$181.37	10.791%	$200.9416	$200.94	$200.95	$200.90
Purchase #4	$161.83	11.563%	$180.5424	$180.54	$180.55	$180.50
Purchase #5	$199.88	8.417%	$216.7039	$216.70	$216.70	$216.70
Purchase #6	$41.43	7.683%	$44.6131	$44.61	$44.60	$44.60
Purchase #7	$199.54	4.813%	$209.1439	$209.14	$209.15	$209.10
7 purchase totals =	$922.93		$998.2824	$998.27	$998.30	$998.10