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	$85.48	6.318%	$90.8806	$90.88	$90.90	$90.90
Purchase #2	$87.99	11.728%	$98.3095	$98.31	$98.30	$98.30
Purchase #3	$81.90	9.816%	$89.9393	$89.94	$89.95	$89.90
Purchase #4	$166.70	6.330%	$177.2521	$177.25	$177.25	$177.30
Purchase #5	$31.67	7.789%	$34.1368	$34.14	$34.15	$34.10
Purchase #6	$75.74	8.538%	$82.2067	$82.21	$82.20	$82.20
Purchase #7	$99.86	8.513%	$108.3611	$108.36	$108.35	$108.40
7 purchase totals =	$629.34		$681.0861	$681.09	$681.10	$681.10