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	$27.30	9.517%	$29.8981	$29.90	$29.90	$29.90
Purchase #2	$55.76	6.389%	$59.3225	$59.32	$59.30	$59.30
Purchase #3	$194.59	7.868%	$209.9003	$209.90	$209.90	$209.90
Purchase #4	$213.82	4.394%	$223.2153	$223.22	$223.20	$223.20
Purchase #5	$163.33	3.823%	$169.5741	$169.57	$169.55	$169.60
Purchase #6	$112.83	5.455%	$118.9849	$118.98	$119.00	$119.00
Purchase #7	$84.30	7.135%	$90.3148	$90.31	$90.30	$90.30
7 purchase totals =	$851.93		$901.2100	$901.20	$901.15	$901.20