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	$123.85	6.135%	$131.4482	$131.45	$131.45	$131.40
Purchase #2	$110.56	9.382%	$120.9327	$120.93	$120.95	$120.90
Purchase #3	$164.50	11.550%	$183.4998	$183.50	$183.50	$183.50
Purchase #4	$139.91	4.234%	$145.8338	$145.83	$145.85	$145.80
Purchase #5	$51.69	6.326%	$54.9599	$54.96	$54.95	$55.00
Purchase #6	$153.91	11.630%	$171.8097	$171.81	$171.80	$171.80
Purchase #7	$104.71	12.705%	$118.0134	$118.01	$118.00	$118.00
7 purchase totals =	$849.13		$926.4975	$926.49	$926.50	$926.40