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	$42.47	12.330%	$47.7066	$47.71	$47.70	$47.70
Purchase #2	$52.53	9.415%	$57.4757	$57.48	$57.50	$57.50
Purchase #3	$116.84	8.402%	$126.6569	$126.66	$126.65	$126.70
Purchase #4	$106.92	6.481%	$113.8495	$113.85	$113.85	$113.80
Purchase #5	$137.57	13.625%	$156.3139	$156.31	$156.30	$156.30
Purchase #6	$118.31	10.145%	$130.3125	$130.31	$130.30	$130.30
Purchase #7	$31.85	4.317%	$33.225	$33.23	$33.25	$33.20
7 purchase totals =	$606.49		$665.5401	$665.55	$665.55	$665.50