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	$102.30	10.761%	$113.3085	$113.31	$113.30	$113.30
Purchase #2	$179.79	5.818%	$190.2502	$190.25	$190.25	$190.30
Purchase #3	$110.82	3.134%	$114.2931	$114.29	$114.30	$114.30
Purchase #4	$41.59	3.238%	$42.9367	$42.94	$42.95	$42.90
Purchase #5	$199.27	5.710%	$210.6483	$210.65	$210.65	$210.60
Purchase #6	$57.51	8.758%	$62.5467	$62.55	$62.55	$62.50
Purchase #7	$86.92	5.243%	$91.4772	$91.48	$91.50	$91.50
7 purchase totals =	$778.20		$825.4607	$825.47	$825.50	$825.40