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	$38.94	9.431%	$42.6124	$42.61	$42.60	$42.60
Purchase #2	$70.52	7.270%	$75.6468	$75.65	$75.65	$75.60
Purchase #3	$174.55	5.691%	$184.4836	$184.48	$184.50	$184.50
Purchase #4	$92.34	13.155%	$104.4873	$104.49	$104.50	$104.50
Purchase #5	$209.65	4.633%	$219.3631	$219.36	$219.35	$219.40
Purchase #6	$143.70	11.238%	$159.849	$159.85	$159.85	$159.80
Purchase #7	$191.96	12.296%	$215.5634	$215.56	$215.55	$215.60
7 purchase totals =	$921.66		$1,002.0056	$1,002.00	$1,002.00	$1,002.00