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	$130.46	12.281%	$146.4818	$146.48	$146.50	$146.50
Purchase #2	$33.34	5.275%	$35.0987	$35.10	$35.10	$35.10
Purchase #3	$213.77	8.151%	$231.1944	$231.19	$231.20	$231.20
Purchase #4	$185.30	8.183%	$200.4631	$200.46	$200.45	$200.50
Purchase #5	$158.63	12.823%	$178.9711	$178.97	$178.95	$179.00
Purchase #6	$198.42	10.174%	$218.6073	$218.61	$218.60	$218.60
Purchase #7	$203.58	9.432%	$222.7817	$222.78	$222.80	$222.80
7 purchase totals =	$1,123.50		$1,233.5981	$1,233.59	$1,233.60	$1,233.70