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	$151.48	11.123%	$168.3291	$168.33	$168.35	$168.30
Purchase #2	$186.80	7.228%	$200.3019	$200.30	$200.30	$200.30
Purchase #3	$35.26	13.361%	$39.9711	$39.97	$39.95	$40.00
Purchase #4	$34.90	11.141%	$38.7882	$38.79	$38.80	$38.80
Purchase #5	$216.37	4.250%	$225.5657	$225.57	$225.55	$225.60
Purchase #6	$40.82	11.308%	$45.4359	$45.44	$45.45	$45.40
Purchase #7	$213.48	11.197%	$237.3834	$237.38	$237.40	$237.40
7 purchase totals =	$879.11		$955.7753	$955.78	$955.80	$955.80