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	$102.71	12.175%	$115.2149	$115.21	$115.20	$115.20
Purchase #2	$36.45	11.795%	$40.7493	$40.75	$40.75	$40.70
Purchase #3	$92.40	8.824%	$100.5534	$100.55	$100.55	$100.60
Purchase #4	$112.98	5.337%	$119.0097	$119.01	$119.00	$119.00
Purchase #5	$105.56	12.216%	$118.4552	$118.46	$118.45	$118.50
Purchase #6	$72.44	3.386%	$74.8928	$74.89	$74.90	$74.90
Purchase #7	$69.67	12.186%	$78.16	$78.16	$78.15	$78.20
7 purchase totals =	$592.21		$647.0353	$647.03	$647.00	$647.10