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	$81.78	7.859%	$88.2071	$88.21	$88.20	$88.20
Purchase #2	$209.31	4.211%	$218.124	$218.12	$218.10	$218.10
Purchase #3	$94.40	6.265%	$100.3142	$100.31	$100.30	$100.30
Purchase #4	$213.62	4.149%	$222.4831	$222.48	$222.50	$222.50
Purchase #5	$199.43	8.396%	$216.1741	$216.17	$216.15	$216.20
Purchase #6	$163.45	12.194%	$183.3811	$183.38	$183.40	$183.40
Purchase #7	$19.93	12.638%	$22.4488	$22.45	$22.45	$22.40
7 purchase totals =	$981.92		$1,051.1324	$1,051.12	$1,051.10	$1,051.10