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	$40.72	12.534%	$45.8238	$45.82	$45.80	$45.80
Purchase #2	$45.43	13.180%	$51.4177	$51.42	$51.40	$51.40
Purchase #3	$78.41	3.218%	$80.9332	$80.93	$80.95	$80.90
Purchase #4	$203.32	9.780%	$223.2047	$223.20	$223.20	$223.20
Purchase #5	$171.96	7.215%	$184.3669	$184.37	$184.35	$184.40
Purchase #6	$110.96	13.466%	$125.9019	$125.90	$125.90	$125.90
Purchase #7	$139.82	6.185%	$148.4679	$148.47	$148.45	$148.50
7 purchase totals =	$790.62		$860.1161	$860.11	$860.05	$860.10