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	$90.73	9.628%	$99.4655	$99.47	$99.45	$99.50
Purchase #2	$143.64	9.853%	$157.7928	$157.79	$157.80	$157.80
Purchase #3	$213.29	12.340%	$239.61	$239.61	$239.60	$239.60
Purchase #4	$38.28	10.825%	$42.4238	$42.42	$42.40	$42.40
Purchase #5	$167.25	12.263%	$187.7599	$187.76	$187.75	$187.80
Purchase #6	$185.86	12.172%	$208.4829	$208.48	$208.50	$208.50
Purchase #7	$171.44	9.709%	$188.0851	$188.09	$188.10	$188.10
7 purchase totals =	$1,010.49		$1,123.6200	$1,123.62	$1,123.60	$1,123.70