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	$244.91	11.236%	$272.4281	$272.43	$272.45	$272.40
Purchase #2	$91.73	13.248%	$103.8824	$103.88	$103.90	$103.90
Purchase #3	$165.69	12.263%	$186.0086	$186.01	$186.00	$186.00
Purchase #4	$183.83	7.467%	$197.5566	$197.56	$197.55	$197.60
Purchase #5	$69.56	5.132%	$73.1298	$73.13	$73.15	$73.10
Purchase #6	$73.73	12.536%	$82.9728	$82.97	$82.95	$83.00
Purchase #7	$83.72	8.502%	$90.8379	$90.84	$90.85	$90.80
7 purchase totals =	$913.17		$1,006.8162	$1,006.82	$1,006.85	$1,006.80