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	$105.34	3.803%	$109.3461	$109.35	$109.35	$109.30
Purchase #2	$60.57	6.386%	$64.438	$64.44	$64.45	$64.40
Purchase #3	$207.35	9.725%	$227.5148	$227.51	$227.50	$227.50
Purchase #4	$242.67	11.317%	$270.133	$270.13	$270.15	$270.10
Purchase #5	$27.85	6.635%	$29.6978	$29.70	$29.70	$29.70
Purchase #6	$158.94	6.388%	$169.0931	$169.09	$169.10	$169.10
Purchase #7	$174.43	12.468%	$196.1779	$196.18	$196.20	$196.20
7 purchase totals =	$977.15		$1,066.4007	$1,066.40	$1,066.45	$1,066.30