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	$35.79	11.365%	$39.8575	$39.86	$39.85	$39.90
Purchase #2	$75.39	10.357%	$83.1981	$83.20	$83.20	$83.20
Purchase #3	$86.36	12.238%	$96.9287	$96.93	$96.95	$96.90
Purchase #4	$116.69	3.508%	$120.7835	$120.78	$120.80	$120.80
Purchase #5	$207.31	11.674%	$231.5114	$231.51	$231.50	$231.50
Purchase #6	$168.41	10.317%	$185.7849	$185.78	$185.80	$185.80
Purchase #7	$52.36	7.720%	$56.4022	$56.40	$56.40	$56.40
7 purchase totals =	$742.31		$814.4663	$814.46	$814.50	$814.50