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	$70.25	11.337%	$78.2142	$78.21	$78.20	$78.20
Purchase #2	$55.65	5.526%	$58.7252	$58.73	$58.75	$58.70
Purchase #3	$164.73	10.235%	$181.5901	$181.59	$181.60	$181.60
Purchase #4	$99.91	12.546%	$112.4447	$112.44	$112.45	$112.40
Purchase #5	$31.71	12.428%	$35.6509	$35.65	$35.65	$35.70
Purchase #6	$195.69	4.214%	$203.9364	$203.94	$203.95	$203.90
Purchase #7	$81.40	10.607%	$90.0341	$90.03	$90.05	$90.00
7 purchase totals =	$699.34		$760.5956	$760.59	$760.65	$760.50