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	$248.82	8.868%	$270.8854	$270.89	$270.90	$270.90
Purchase #2	$36.65	9.735%	$40.2179	$40.22	$40.20	$40.20
Purchase #3	$141.25	7.677%	$152.0938	$152.09	$152.10	$152.10
Purchase #4	$137.72	11.734%	$153.8801	$153.88	$153.90	$153.90
Purchase #5	$88.57	11.755%	$98.9814	$98.98	$99.00	$99.00
Purchase #6	$11.88	13.854%	$13.5259	$13.53	$13.55	$13.50
Purchase #7	$99.41	9.693%	$109.0458	$109.05	$109.05	$109.00
7 purchase totals =	$764.30		$838.6303	$838.64	$838.70	$838.60