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	$44.92	13.331%	$50.9083	$50.91	$50.90	$50.90
Purchase #2	$228.46	5.569%	$241.1829	$241.18	$241.20	$241.20
Purchase #3	$125.90	13.155%	$142.4621	$142.46	$142.45	$142.50
Purchase #4	$130.40	9.148%	$142.329	$142.33	$142.35	$142.30
Purchase #5	$198.82	6.480%	$211.7035	$211.70	$211.70	$211.70
Purchase #6	$115.25	3.269%	$119.0175	$119.02	$119.00	$119.00
Purchase #7	$155.47	3.413%	$160.7762	$160.78	$160.80	$160.80
7 purchase totals =	$999.22		$1,068.3795	$1,068.38	$1,068.40	$1,068.40