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	$28.56	10.130%	$31.4531	$31.45	$31.45	$31.50
Purchase #2	$167.70	8.215%	$181.4766	$181.48	$181.50	$181.50
Purchase #3	$100.38	9.468%	$109.884	$109.88	$109.90	$109.90
Purchase #4	$53.44	5.212%	$56.2253	$56.23	$56.25	$56.20
Purchase #5	$137.29	8.439%	$148.8759	$148.88	$148.90	$148.90
Purchase #6	$155.38	3.272%	$160.464	$160.46	$160.45	$160.50
Purchase #7	$51.85	5.166%	$54.5286	$54.53	$54.55	$54.50
7 purchase totals =	$694.60		$742.9075	$742.91	$743.00	$743.00