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	$163.39	13.383%	$185.2565	$185.26	$185.25	$185.30
Purchase #2	$50.38	8.839%	$54.8331	$54.83	$54.85	$54.80
Purchase #3	$189.26	10.853%	$209.8004	$209.80	$209.80	$209.80
Purchase #4	$112.44	3.300%	$116.1505	$116.15	$116.15	$116.20
Purchase #5	$52.90	8.807%	$57.5589	$57.56	$57.55	$57.60
Purchase #6	$66.72	11.355%	$74.2961	$74.30	$74.30	$74.30
Purchase #7	$200.67	7.630%	$215.9811	$215.98	$216.00	$216.00
7 purchase totals =	$835.76		$913.8766	$913.88	$913.90	$914.00