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	$57.72	3.803%	$59.9151	$59.92	$59.90	$59.90
Purchase #2	$59.78	7.300%	$64.1439	$64.14	$64.15	$64.10
Purchase #3	$58.73	9.400%	$64.2506	$64.25	$64.25	$64.30
Purchase #4	$22.82	3.181%	$23.5459	$23.55	$23.55	$23.50
Purchase #5	$228.83	13.172%	$258.9715	$258.97	$258.95	$259.00
Purchase #6	$108.72	11.586%	$121.3163	$121.32	$121.30	$121.30
Purchase #7	$7.44	5.572%	$7.8546	$7.85	$7.85	$7.90
7 purchase totals =	$544.04		$599.9979	$600.00	$599.95	$600.00