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	$18.92	8.266%	$20.4839	$20.48	$20.50	$20.50
Purchase #2	$132.50	6.819%	$141.5352	$141.54	$141.55	$141.50
Purchase #3	$228.74	9.696%	$250.9186	$250.92	$250.90	$250.90
Purchase #4	$44.92	12.124%	$50.3661	$50.37	$50.35	$50.40
Purchase #5	$210.55	6.398%	$224.021	$224.02	$224.00	$224.00
Purchase #6	$186.91	5.180%	$196.5919	$196.59	$196.60	$196.60
Purchase #7	$119.82	4.837%	$125.6157	$125.62	$125.60	$125.60
7 purchase totals =	$942.36		$1,009.5324	$1,009.54	$1,009.50	$1,009.50