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	$67.93	6.610%	$72.4202	$72.42	$72.40	$72.40
Purchase #2	$187.91	12.779%	$211.923	$211.92	$211.90	$211.90
Purchase #3	$28.42	11.273%	$31.6238	$31.62	$31.60	$31.60
Purchase #4	$187.62	11.381%	$208.973	$208.97	$208.95	$209.00
Purchase #5	$90.63	13.341%	$102.7209	$102.72	$102.70	$102.70
Purchase #6	$173.89	5.158%	$182.8592	$182.86	$182.85	$182.90
Purchase #7	$124.84	9.425%	$136.6062	$136.61	$136.60	$136.60
7 purchase totals =	$861.24		$947.1263	$947.12	$947.00	$947.10