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	$233.32	7.146%	$249.993	$249.99	$250.00	$250.00
Purchase #2	$114.31	3.153%	$117.9142	$117.91	$117.90	$117.90
Purchase #3	$7.77	13.441%	$8.8144	$8.81	$8.80	$8.80
Purchase #4	$88.48	3.284%	$91.3857	$91.39	$91.40	$91.40
Purchase #5	$101.38	7.648%	$109.1335	$109.13	$109.15	$109.10
Purchase #6	$84.89	8.565%	$92.1608	$92.16	$92.15	$92.20
Purchase #7	$96.35	4.602%	$100.784	$100.78	$100.80	$100.80
7 purchase totals =	$726.50		$770.1856	$770.17	$770.20	$770.20