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	$120.98	12.598%	$136.2211	$136.22	$136.20	$136.20
Purchase #2	$104.79	6.507%	$111.6087	$111.61	$111.60	$111.60
Purchase #3	$45.27	12.293%	$50.835	$50.84	$50.85	$50.80
Purchase #4	$59.32	12.384%	$66.6662	$66.67	$66.65	$66.70
Purchase #5	$130.84	13.776%	$148.8645	$148.86	$148.85	$148.90
Purchase #6	$128.33	12.367%	$144.2006	$144.20	$144.20	$144.20
Purchase #7	$186.53	12.336%	$209.5403	$209.54	$209.55	$209.50
7 purchase totals =	$776.06		$867.9364	$867.94	$867.90	$867.90