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	$38.40	3.270%	$39.6557	$39.66	$39.65	$39.70
Purchase #2	$14.99	5.511%	$15.8161	$15.82	$15.80	$15.80
Purchase #3	$74.98	10.512%	$82.8619	$82.86	$82.85	$82.90
Purchase #4	$29.77	7.755%	$32.0787	$32.08	$32.10	$32.10
Purchase #5	$201.56	10.112%	$221.9417	$221.94	$221.95	$221.90
Purchase #6	$39.32	10.598%	$43.4871	$43.49	$43.50	$43.50
Purchase #7	$92.31	8.402%	$100.0659	$100.07	$100.05	$100.10
7 purchase totals =	$491.33		$535.9071	$535.92	$535.90	$536.00