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	$119.50	3.614%	$123.8187	$123.82	$123.80	$123.80
Purchase #2	$69.63	3.304%	$71.9306	$71.93	$71.95	$71.90
Purchase #3	$218.50	11.509%	$243.6472	$243.65	$243.65	$243.60
Purchase #4	$153.59	9.434%	$168.0797	$168.08	$168.10	$168.10
Purchase #5	$171.74	3.315%	$177.4332	$177.43	$177.45	$177.40
Purchase #6	$63.75	12.240%	$71.553	$71.55	$71.55	$71.60
Purchase #7	$129.73	8.715%	$141.036	$141.04	$141.05	$141.00
7 purchase totals =	$926.44		$997.4984	$997.50	$997.55	$997.40