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	$229.89	3.587%	$238.1362	$238.14	$238.15	$238.10
Purchase #2	$38.96	8.184%	$42.1485	$42.15	$42.15	$42.10
Purchase #3	$162.79	13.718%	$185.1215	$185.12	$185.10	$185.10
Purchase #4	$38.56	10.212%	$42.4977	$42.50	$42.50	$42.50
Purchase #5	$217.90	11.131%	$242.1544	$242.15	$242.15	$242.20
Purchase #6	$189.76	10.236%	$209.1838	$209.18	$209.20	$209.20
Purchase #7	$81.48	3.570%	$84.3888	$84.39	$84.40	$84.40
7 purchase totals =	$959.34		$1,043.6309	$1,043.63	$1,043.65	$1,043.60