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	$90.34	9.478%	$98.9024	$98.90	$98.90	$98.90
Purchase #2	$67.76	7.800%	$73.0453	$73.05	$73.05	$73.00
Purchase #3	$66.39	6.266%	$70.55	$70.55	$70.55	$70.60
Purchase #4	$156.67	5.459%	$165.2226	$165.22	$165.20	$165.20
Purchase #5	$156.92	3.858%	$162.974	$162.97	$162.95	$163.00
Purchase #6	$113.73	12.273%	$127.6881	$127.69	$127.70	$127.70
Purchase #7	$144.84	5.744%	$153.1596	$153.16	$153.15	$153.20
7 purchase totals =	$796.65		$851.5420	$851.54	$851.50	$851.60