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	$98.33	11.623%	$109.7589	$109.76	$109.75	$109.80
Purchase #2	$167.69	13.148%	$189.7379	$189.74	$189.75	$189.70
Purchase #3	$122.28	7.274%	$131.1746	$131.17	$131.15	$131.20
Purchase #4	$132.88	6.296%	$141.2461	$141.25	$141.25	$141.20
Purchase #5	$176.52	3.314%	$182.3699	$182.37	$182.35	$182.40
Purchase #6	$131.92	7.429%	$141.7203	$141.72	$141.70	$141.70
Purchase #7	$90.83	13.152%	$102.776	$102.78	$102.80	$102.80
7 purchase totals =	$920.45		$998.7837	$998.79	$998.75	$998.80