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	$131.72	3.379%	$136.1708	$136.17	$136.15	$136.20
Purchase #2	$144.75	10.217%	$159.5391	$159.54	$159.55	$159.50
Purchase #3	$148.87	13.242%	$168.5834	$168.58	$168.60	$168.60
Purchase #4	$231.54	11.497%	$258.1602	$258.16	$258.15	$258.20
Purchase #5	$30.79	8.320%	$33.3517	$33.35	$33.35	$33.40
Purchase #6	$38.51	10.134%	$42.4126	$42.41	$42.40	$42.40
Purchase #7	$246.37	8.528%	$267.3804	$267.38	$267.40	$267.40
7 purchase totals =	$972.55		$1,065.5982	$1,065.59	$1,065.60	$1,065.70