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	$134.48	7.238%	$144.2137	$144.21	$144.20	$144.20
Purchase #2	$215.79	12.272%	$242.2717	$242.27	$242.25	$242.30
Purchase #3	$79.78	12.739%	$89.9432	$89.94	$89.95	$89.90
Purchase #4	$131.81	12.812%	$148.6975	$148.70	$148.70	$148.70
Purchase #5	$93.29	10.339%	$102.9353	$102.94	$102.95	$102.90
Purchase #6	$148.32	10.819%	$164.3667	$164.37	$164.35	$164.40
Purchase #7	$167.36	12.273%	$187.9001	$187.90	$187.90	$187.90
7 purchase totals =	$970.83		$1,080.3282	$1,080.33	$1,080.30	$1,080.30