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	$77.46	9.209%	$84.5933	$84.59	$84.60	$84.60
Purchase #2	$98.90	4.632%	$103.481	$103.48	$103.50	$103.50
Purchase #3	$182.65	11.574%	$203.7899	$203.79	$203.80	$203.80
Purchase #4	$51.66	11.184%	$57.4377	$57.44	$57.45	$57.40
Purchase #5	$40.89	6.160%	$43.4088	$43.41	$43.40	$43.40
Purchase #6	$192.34	9.426%	$210.47	$210.47	$210.45	$210.50
Purchase #7	$219.91	13.700%	$250.0377	$250.04	$250.05	$250.00
7 purchase totals =	$863.81		$953.2184	$953.22	$953.25	$953.20