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	$80.33	3.441%	$83.0942	$83.09	$83.10	$83.10
Purchase #2	$90.38	11.161%	$100.4673	$100.47	$100.45	$100.50
Purchase #3	$182.41	8.333%	$197.6102	$197.61	$197.60	$197.60
Purchase #4	$98.48	7.427%	$105.7941	$105.79	$105.80	$105.80
Purchase #5	$211.38	13.609%	$240.1467	$240.15	$240.15	$240.10
Purchase #6	$150.55	9.503%	$164.8568	$164.86	$164.85	$164.90
Purchase #7	$143.58	3.381%	$148.4344	$148.43	$148.45	$148.40
7 purchase totals =	$957.11		$1,040.4037	$1,040.40	$1,040.40	$1,040.40