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	$63.82	13.673%	$72.5461	$72.55	$72.55	$72.50
Purchase #2	$43.66	9.758%	$47.9203	$47.92	$47.90	$47.90
Purchase #3	$143.99	8.279%	$155.9109	$155.91	$155.90	$155.90
Purchase #4	$111.97	6.740%	$119.5168	$119.52	$119.50	$119.50
Purchase #5	$139.25	3.480%	$144.0959	$144.10	$144.10	$144.10
Purchase #6	$190.39	9.269%	$208.0372	$208.04	$208.05	$208.00
Purchase #7	$188.72	7.834%	$203.5043	$203.50	$203.50	$203.50
7 purchase totals =	$881.80		$951.5315	$951.54	$951.50	$951.40