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	$53.37	7.770%	$57.5168	$57.52	$57.50	$57.50
Purchase #2	$103.79	5.192%	$109.1788	$109.18	$109.20	$109.20
Purchase #3	$213.45	4.652%	$223.3797	$223.38	$223.40	$223.40
Purchase #4	$77.88	12.152%	$87.344	$87.34	$87.35	$87.30
Purchase #5	$131.65	7.451%	$141.4592	$141.46	$141.45	$141.50
Purchase #6	$121.48	9.243%	$132.7084	$132.71	$132.70	$132.70
Purchase #7	$210.38	9.148%	$229.6256	$229.63	$229.65	$229.60
7 purchase totals =	$912.00		$981.2125	$981.22	$981.25	$981.20