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	$38.54	10.196%	$42.4695	$42.47	$42.45	$42.50
Purchase #2	$8.97	12.483%	$10.0897	$10.09	$10.10	$10.10
Purchase #3	$39.30	9.871%	$43.1793	$43.18	$43.20	$43.20
Purchase #4	$176.81	12.215%	$198.4073	$198.41	$198.40	$198.40
Purchase #5	$119.27	6.757%	$127.3291	$127.33	$127.35	$127.30
Purchase #6	$152.62	7.620%	$164.2496	$164.25	$164.25	$164.20
Purchase #7	$98.51	10.608%	$108.9599	$108.96	$108.95	$109.00
7 purchase totals =	$634.02		$694.6844	$694.69	$694.70	$694.70