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	$41.33	4.337%	$43.1225	$43.12	$43.10	$43.10
Purchase #2	$248.34	3.654%	$257.4143	$257.41	$257.40	$257.40
Purchase #3	$130.62	12.823%	$147.3694	$147.37	$147.35	$147.40
Purchase #4	$30.54	3.539%	$31.6208	$31.62	$31.60	$31.60
Purchase #5	$152.76	8.357%	$165.5262	$165.53	$165.55	$165.50
Purchase #6	$168.45	13.475%	$191.1486	$191.15	$191.15	$191.10
Purchase #7	$30.45	11.699%	$34.0123	$34.01	$34.00	$34.00
7 purchase totals =	$802.49		$870.2141	$870.21	$870.15	$870.10