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	$128.47	8.199%	$139.0033	$139.00	$139.00	$139.00
Purchase #2	$124.34	7.300%	$133.4168	$133.42	$133.40	$133.40
Purchase #3	$222.73	11.578%	$248.5177	$248.52	$248.50	$248.50
Purchase #4	$124.43	12.264%	$139.6901	$139.69	$139.70	$139.70
Purchase #5	$196.53	7.340%	$210.9553	$210.96	$210.95	$211.00
Purchase #6	$79.45	12.127%	$89.0849	$89.08	$89.10	$89.10
Purchase #7	$119.59	10.676%	$132.3574	$132.36	$132.35	$132.40
7 purchase totals =	$995.54		$1,093.0255	$1,093.03	$1,093.00	$1,093.10