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	$234.90	4.169%	$244.693	$244.69	$244.70	$244.70
Purchase #2	$99.62	3.201%	$102.8088	$102.81	$102.80	$102.80
Purchase #3	$47.55	6.724%	$50.7473	$50.75	$50.75	$50.70
Purchase #4	$147.31	11.688%	$164.5276	$164.53	$164.55	$164.50
Purchase #5	$224.82	12.541%	$253.0147	$253.01	$253.00	$253.00
Purchase #6	$56.49	9.548%	$61.8837	$61.88	$61.90	$61.90
Purchase #7	$191.82	11.520%	$213.9177	$213.92	$213.90	$213.90
7 purchase totals =	$1,002.51		$1,091.5928	$1,091.59	$1,091.60	$1,091.50