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	$175.37	3.822%	$182.0726	$182.07	$182.05	$182.10
Purchase #2	$141.81	5.859%	$150.1186	$150.12	$150.10	$150.10
Purchase #3	$247.32	12.796%	$278.9671	$278.97	$278.95	$279.00
Purchase #4	$80.89	11.126%	$89.8898	$89.89	$89.90	$89.90
Purchase #5	$223.29	7.577%	$240.2087	$240.21	$240.20	$240.20
Purchase #6	$12.61	4.811%	$13.2167	$13.22	$13.20	$13.20
Purchase #7	$104.32	7.416%	$112.0564	$112.06	$112.05	$112.10
7 purchase totals =	$985.61		$1,066.5299	$1,066.54	$1,066.45	$1,066.60