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	$81.49	9.871%	$89.5339	$89.53	$89.55	$89.50
Purchase #2	$132.67	3.446%	$137.2418	$137.24	$137.25	$137.20
Purchase #3	$178.46	3.471%	$184.6543	$184.65	$184.65	$184.70
Purchase #4	$41.97	7.392%	$45.0724	$45.07	$45.05	$45.10
Purchase #5	$9.93	6.480%	$10.5735	$10.57	$10.55	$10.60
Purchase #6	$246.42	11.134%	$273.8564	$273.86	$273.85	$273.90
Purchase #7	$58.88	6.149%	$62.5005	$62.50	$62.50	$62.50
7 purchase totals =	$749.82		$803.4328	$803.42	$803.40	$803.50