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	$106.86	3.400%	$110.4932	$110.49	$110.50	$110.50
Purchase #2	$106.88	11.307%	$118.9649	$118.96	$118.95	$119.00
Purchase #3	$39.71	9.467%	$43.4693	$43.47	$43.45	$43.50
Purchase #4	$170.45	6.801%	$182.0423	$182.04	$182.05	$182.00
Purchase #5	$166.66	12.215%	$187.0175	$187.02	$187.00	$187.00
Purchase #6	$86.38	3.459%	$89.3679	$89.37	$89.35	$89.40
Purchase #7	$101.25	6.422%	$107.7523	$107.75	$107.75	$107.80
7 purchase totals =	$778.19		$839.1074	$839.10	$839.05	$839.20