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	$248.75	12.609%	$280.1149	$280.11	$280.10	$280.10
Purchase #2	$169.48	10.654%	$187.5364	$187.54	$187.55	$187.50
Purchase #3	$72.52	13.159%	$82.0629	$82.06	$82.05	$82.10
Purchase #4	$246.53	9.529%	$270.0218	$270.02	$270.00	$270.00
Purchase #5	$240.89	11.283%	$268.0696	$268.07	$268.05	$268.10
Purchase #6	$156.73	4.800%	$164.253	$164.25	$164.25	$164.30
Purchase #7	$87.78	3.445%	$90.804	$90.80	$90.80	$90.80
7 purchase totals =	$1,222.68		$1,342.8626	$1,342.85	$1,342.80	$1,342.90