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	$115.90	7.394%	$124.4696	$124.47	$124.45	$124.50
Purchase #2	$241.73	11.694%	$269.9979	$270.00	$270.00	$270.00
Purchase #3	$239.80	8.390%	$259.9192	$259.92	$259.90	$259.90
Purchase #4	$142.62	9.729%	$156.4955	$156.50	$156.50	$156.50
Purchase #5	$168.29	10.636%	$186.1893	$186.19	$186.20	$186.20
Purchase #6	$236.66	4.735%	$247.8659	$247.87	$247.85	$247.90
Purchase #7	$51.56	7.563%	$55.4595	$55.46	$55.45	$55.50
7 purchase totals =	$1,196.56		$1,300.3969	$1,300.41	$1,300.35	$1,300.50