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	$200.69	10.376%	$221.5136	$221.51	$221.50	$221.50
Purchase #2	$181.69	3.601%	$188.2327	$188.23	$188.25	$188.20
Purchase #3	$199.89	13.332%	$226.5393	$226.54	$226.55	$226.50
Purchase #4	$34.45	12.831%	$38.8703	$38.87	$38.85	$38.90
Purchase #5	$56.34	9.844%	$61.8861	$61.89	$61.90	$61.90
Purchase #6	$240.44	11.484%	$268.0521	$268.05	$268.05	$268.10
Purchase #7	$36.58	9.641%	$40.1067	$40.11	$40.10	$40.10
7 purchase totals =	$950.08		$1,045.2008	$1,045.20	$1,045.20	$1,045.20