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	$201.72	9.824%	$221.537	$221.54	$221.55	$221.50
Purchase #2	$133.43	6.294%	$141.8281	$141.83	$141.85	$141.80
Purchase #3	$194.80	12.479%	$219.1091	$219.11	$219.10	$219.10
Purchase #4	$100.29	3.260%	$103.5595	$103.56	$103.55	$103.60
Purchase #5	$202.99	7.302%	$217.8123	$217.81	$217.80	$217.80
Purchase #6	$113.96	8.740%	$123.9201	$123.92	$123.90	$123.90
Purchase #7	$31.72	4.719%	$33.2169	$33.22	$33.20	$33.20
7 purchase totals =	$978.91		$1,060.9830	$1,060.99	$1,060.95	$1,060.90