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	$155.31	7.179%	$166.4597	$166.46	$166.45	$166.50
Purchase #2	$122.90	3.836%	$127.6144	$127.61	$127.60	$127.60
Purchase #3	$100.85	11.796%	$112.7463	$112.75	$112.75	$112.70
Purchase #4	$189.59	11.220%	$210.862	$210.86	$210.85	$210.90
Purchase #5	$76.48	9.862%	$84.0225	$84.02	$84.00	$84.00
Purchase #6	$189.74	8.281%	$205.4524	$205.45	$205.45	$205.50
Purchase #7	$168.42	12.418%	$189.3344	$189.33	$189.35	$189.30
7 purchase totals =	$1,003.29		$1,096.4917	$1,096.48	$1,096.45	$1,096.50