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	$40.63	9.257%	$44.3911	$44.39	$44.40	$44.40
Purchase #2	$83.60	7.289%	$89.6936	$89.69	$89.70	$89.70
Purchase #3	$250.29	12.712%	$282.1069	$282.11	$282.10	$282.10
Purchase #4	$77.84	5.870%	$82.4092	$82.41	$82.40	$82.40
Purchase #5	$16.46	9.427%	$18.0117	$18.01	$18.00	$18.00
Purchase #6	$159.57	9.534%	$174.7834	$174.78	$174.80	$174.80
Purchase #7	$215.46	3.453%	$222.8998	$222.90	$222.90	$222.90
7 purchase totals =	$843.85		$914.2957	$914.29	$914.30	$914.30