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	$112.75	13.483%	$127.9521	$127.95	$127.95	$128.00
Purchase #2	$18.62	13.421%	$21.119	$21.12	$21.10	$21.10
Purchase #3	$249.89	13.615%	$283.9125	$283.91	$283.90	$283.90
Purchase #4	$213.27	5.197%	$224.3536	$224.35	$224.35	$224.40
Purchase #5	$239.92	9.114%	$261.7863	$261.79	$261.80	$261.80
Purchase #6	$86.44	6.365%	$91.9419	$91.94	$91.95	$91.90
Purchase #7	$102.89	9.399%	$112.5606	$112.56	$112.55	$112.60
7 purchase totals =	$1,023.78		$1,123.6260	$1,123.62	$1,123.60	$1,123.70