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	$53.79	7.274%	$57.7027	$57.70	$57.70	$57.70
Purchase #2	$113.82	9.321%	$124.4292	$124.43	$124.45	$124.40
Purchase #3	$88.43	4.634%	$92.5278	$92.53	$92.55	$92.50
Purchase #4	$167.32	11.384%	$186.3677	$186.37	$186.35	$186.40
Purchase #5	$133.83	12.547%	$150.6217	$150.62	$150.60	$150.60
Purchase #6	$164.69	8.867%	$179.2931	$179.29	$179.30	$179.30
Purchase #7	$155.33	9.374%	$169.8906	$169.89	$169.90	$169.90
7 purchase totals =	$877.21		$960.8328	$960.83	$960.85	$960.80