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	$131.66	7.755%	$141.8702	$141.87	$141.85	$141.90
Purchase #2	$175.28	7.226%	$187.9457	$187.95	$187.95	$187.90
Purchase #3	$110.63	11.560%	$123.4188	$123.42	$123.40	$123.40
Purchase #4	$57.32	11.338%	$63.8189	$63.82	$63.80	$63.80
Purchase #5	$70.96	10.326%	$78.2873	$78.29	$78.30	$78.30
Purchase #6	$5.39	12.344%	$6.0553	$6.06	$6.05	$6.10
Purchase #7	$215.53	12.482%	$242.4325	$242.43	$242.45	$242.40
7 purchase totals =	$766.77		$843.8287	$843.84	$843.80	$843.80