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	$238.90	9.388%	$261.3279	$261.33	$261.35	$261.30
Purchase #2	$174.42	4.640%	$182.5131	$182.51	$182.50	$182.50
Purchase #3	$93.41	4.648%	$97.7517	$97.75	$97.75	$97.80
Purchase #4	$131.57	9.426%	$143.9718	$143.97	$143.95	$144.00
Purchase #5	$40.52	7.533%	$43.5724	$43.57	$43.55	$43.60
Purchase #6	$57.70	3.608%	$59.7818	$59.78	$59.80	$59.80
Purchase #7	$188.84	12.219%	$211.9144	$211.91	$211.90	$211.90
7 purchase totals =	$925.36		$1,000.8331	$1,000.82	$1,000.80	$1,000.90