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	$91.55	13.801%	$104.1848	$104.18	$104.20	$104.20
Purchase #2	$32.57	13.235%	$36.8806	$36.88	$36.90	$36.90
Purchase #3	$227.25	9.122%	$247.9797	$247.98	$248.00	$248.00
Purchase #4	$121.33	9.173%	$132.4596	$132.46	$132.45	$132.50
Purchase #5	$82.76	12.229%	$92.8807	$92.88	$92.90	$92.90
Purchase #6	$137.65	4.686%	$144.1003	$144.10	$144.10	$144.10
Purchase #7	$206.79	6.339%	$219.8984	$219.90	$219.90	$219.90
7 purchase totals =	$899.90		$978.3841	$978.38	$978.45	$978.50