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	$92.51	6.861%	$98.8571	$98.86	$98.85	$98.90
Purchase #2	$114.72	11.310%	$127.6948	$127.69	$127.70	$127.70
Purchase #3	$245.60	9.484%	$268.8927	$268.89	$268.90	$268.90
Purchase #4	$36.36	10.577%	$40.2058	$40.21	$40.20	$40.20
Purchase #5	$83.67	6.679%	$89.2583	$89.26	$89.25	$89.30
Purchase #6	$29.78	9.674%	$32.6609	$32.66	$32.65	$32.70
Purchase #7	$163.72	8.416%	$177.4987	$177.50	$177.50	$177.50
7 purchase totals =	$766.36		$835.0683	$835.07	$835.05	$835.20