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	$78.63	12.599%	$88.5366	$88.54	$88.55	$88.50
Purchase #2	$139.71	10.312%	$154.1169	$154.12	$154.10	$154.10
Purchase #3	$238.67	8.284%	$258.4414	$258.44	$258.45	$258.40
Purchase #4	$65.45	5.590%	$69.1087	$69.11	$69.10	$69.10
Purchase #5	$57.88	11.498%	$64.535	$64.54	$64.55	$64.50
Purchase #6	$116.43	9.540%	$127.5374	$127.54	$127.55	$127.50
Purchase #7	$163.64	4.213%	$170.5342	$170.53	$170.55	$170.50
7 purchase totals =	$860.41		$932.8102	$932.82	$932.85	$932.60