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	$136.41	7.498%	$146.638	$146.64	$146.65	$146.60
Purchase #2	$47.96	10.509%	$53.0001	$53.00	$53.00	$53.00
Purchase #3	$68.57	6.735%	$73.1882	$73.19	$73.20	$73.20
Purchase #4	$123.80	13.836%	$140.929	$140.93	$140.95	$140.90
Purchase #5	$84.93	6.645%	$90.5736	$90.57	$90.55	$90.60
Purchase #6	$84.26	5.663%	$89.0316	$89.03	$89.05	$89.00
Purchase #7	$39.78	8.835%	$43.2946	$43.29	$43.30	$43.30
7 purchase totals =	$585.71		$636.6551	$636.65	$636.70	$636.60