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	$220.68	11.582%	$246.2392	$246.24	$246.25	$246.20
Purchase #2	$63.49	9.398%	$69.4568	$69.46	$69.45	$69.50
Purchase #3	$210.48	9.458%	$230.3872	$230.39	$230.40	$230.40
Purchase #4	$99.80	11.617%	$111.3938	$111.39	$111.40	$111.40
Purchase #5	$168.65	3.794%	$175.0486	$175.05	$175.05	$175.00
Purchase #6	$215.98	3.511%	$223.5631	$223.56	$223.55	$223.60
Purchase #7	$80.42	12.415%	$90.4041	$90.40	$90.40	$90.40
7 purchase totals =	$1,059.50		$1,146.4928	$1,146.49	$1,146.50	$1,146.50