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	$101.46	11.264%	$112.8885	$112.89	$112.90	$112.90
Purchase #2	$83.70	4.265%	$87.2698	$87.27	$87.25	$87.30
Purchase #3	$119.56	9.138%	$130.4854	$130.49	$130.50	$130.50
Purchase #4	$103.47	9.494%	$113.2934	$113.29	$113.30	$113.30
Purchase #5	$133.41	3.334%	$137.8579	$137.86	$137.85	$137.90
Purchase #6	$70.74	11.313%	$78.7428	$78.74	$78.75	$78.70
Purchase #7	$238.91	9.465%	$261.5228	$261.52	$261.50	$261.50
7 purchase totals =	$851.25		$922.0606	$922.06	$922.05	$922.10