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	$86.32	11.782%	$96.4902	$96.49	$96.50	$96.50
Purchase #2	$122.46	5.300%	$128.9504	$128.95	$128.95	$129.00
Purchase #3	$92.88	11.374%	$103.4442	$103.44	$103.45	$103.40
Purchase #4	$216.39	13.732%	$246.1047	$246.10	$246.10	$246.10
Purchase #5	$171.69	5.205%	$180.6265	$180.63	$180.65	$180.60
Purchase #6	$88.35	13.732%	$100.4822	$100.48	$100.50	$100.50
Purchase #7	$185.71	12.870%	$209.6109	$209.61	$209.60	$209.60
7 purchase totals =	$963.80		$1,065.7091	$1,065.70	$1,065.75	$1,065.70