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	$68.76	13.257%	$77.8755	$77.88	$77.90	$77.90
Purchase #2	$14.26	4.693%	$14.9292	$14.93	$14.95	$14.90
Purchase #3	$195.50	6.330%	$207.8752	$207.88	$207.90	$207.90
Purchase #4	$112.86	12.761%	$127.2621	$127.26	$127.25	$127.30
Purchase #5	$88.57	7.625%	$95.3235	$95.32	$95.30	$95.30
Purchase #6	$78.47	9.617%	$86.0165	$86.02	$86.00	$86.00
Purchase #7	$51.33	10.807%	$56.8772	$56.88	$56.90	$56.90
7 purchase totals =	$609.75		$666.1592	$666.17	$666.20	$666.20