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	$31.50	7.304%	$33.8008	$33.80	$33.80	$33.80
Purchase #2	$94.73	8.398%	$102.6854	$102.69	$102.70	$102.70
Purchase #3	$126.53	11.390%	$140.9418	$140.94	$140.95	$140.90
Purchase #4	$56.72	4.861%	$59.4772	$59.48	$59.50	$59.50
Purchase #5	$201.88	3.239%	$208.4189	$208.42	$208.40	$208.40
Purchase #6	$137.27	6.473%	$146.1555	$146.16	$146.15	$146.20
Purchase #7	$57.85	11.171%	$64.3124	$64.31	$64.30	$64.30
7 purchase totals =	$706.48		$755.7920	$755.80	$755.80	$755.80