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	$128.91	4.322%	$134.4815	$134.48	$134.50	$134.50
Purchase #2	$185.97	3.451%	$192.3878	$192.39	$192.40	$192.40
Purchase #3	$158.44	8.269%	$171.5414	$171.54	$171.55	$171.50
Purchase #4	$130.55	13.624%	$148.3361	$148.34	$148.35	$148.30
Purchase #5	$73.31	13.678%	$83.3373	$83.34	$83.35	$83.30
Purchase #6	$138.88	12.737%	$156.5691	$156.57	$156.55	$156.60
Purchase #7	$150.71	6.169%	$160.0073	$160.01	$160.00	$160.00
7 purchase totals =	$966.77		$1,046.6605	$1,046.67	$1,046.70	$1,046.60