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	$125.50	12.544%	$141.2427	$141.24	$141.25	$141.20
Purchase #2	$31.89	3.849%	$33.1174	$33.12	$33.10	$33.10
Purchase #3	$196.73	11.550%	$219.4523	$219.45	$219.45	$219.50
Purchase #4	$64.74	5.397%	$68.234	$68.23	$68.25	$68.20
Purchase #5	$91.84	8.173%	$99.3461	$99.35	$99.35	$99.30
Purchase #6	$36.81	4.281%	$38.3858	$38.39	$38.40	$38.40
Purchase #7	$197.74	12.697%	$222.847	$222.85	$222.85	$222.80
7 purchase totals =	$745.25		$822.6253	$822.63	$822.65	$822.50