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	$45.40	13.635%	$51.5903	$51.59	$51.60	$51.60
Purchase #2	$188.91	9.866%	$207.5479	$207.55	$207.55	$207.50
Purchase #3	$76.41	3.232%	$78.8796	$78.88	$78.90	$78.90
Purchase #4	$245.29	7.690%	$264.1528	$264.15	$264.15	$264.20
Purchase #5	$178.77	12.583%	$201.2646	$201.26	$201.25	$201.30
Purchase #6	$75.43	12.739%	$85.039	$85.04	$85.05	$85.00
Purchase #7	$93.51	12.731%	$105.4148	$105.41	$105.40	$105.40
7 purchase totals =	$903.72		$993.8890	$993.88	$993.90	$993.90