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	$191.34	11.785%	$213.8894	$213.89	$213.90	$213.90
Purchase #2	$86.49	4.553%	$90.4279	$90.43	$90.45	$90.40
Purchase #3	$50.95	3.849%	$52.9111	$52.91	$52.90	$52.90
Purchase #4	$169.39	6.313%	$180.0836	$180.08	$180.10	$180.10
Purchase #5	$245.92	13.824%	$279.916	$279.92	$279.90	$279.90
Purchase #6	$93.58	9.435%	$102.4093	$102.41	$102.40	$102.40
Purchase #7	$247.48	13.284%	$280.3552	$280.36	$280.35	$280.40
7 purchase totals =	$1,085.15		$1,199.9925	$1,200.00	$1,200.00	$1,200.00