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	$140.96	6.423%	$150.0139	$150.01	$150.00	$150.00
Purchase #2	$205.39	12.860%	$231.8032	$231.80	$231.80	$231.80
Purchase #3	$219.62	3.560%	$227.4385	$227.44	$227.45	$227.40
Purchase #4	$141.46	13.676%	$160.8061	$160.81	$160.80	$160.80
Purchase #5	$87.31	13.506%	$99.1021	$99.10	$99.10	$99.10
Purchase #6	$151.50	13.502%	$171.9555	$171.96	$171.95	$172.00
Purchase #7	$196.55	7.139%	$210.5817	$210.58	$210.60	$210.60
7 purchase totals =	$1,142.79		$1,251.7010	$1,251.70	$1,251.70	$1,251.70