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	$122.69	7.386%	$131.7519	$131.75	$131.75	$131.80
Purchase #2	$122.60	12.223%	$137.5854	$137.59	$137.60	$137.60
Purchase #3	$37.94	5.544%	$40.0434	$40.04	$40.05	$40.00
Purchase #4	$58.32	12.276%	$65.4794	$65.48	$65.50	$65.50
Purchase #5	$40.32	13.342%	$45.6995	$45.70	$45.70	$45.70
Purchase #6	$53.86	10.754%	$59.6521	$59.65	$59.65	$59.70
Purchase #7	$116.92	3.194%	$120.6544	$120.65	$120.65	$120.70
7 purchase totals =	$552.65		$600.8661	$600.86	$600.90	$601.00