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	$117.98	11.379%	$131.4049	$131.40	$131.40	$131.40
Purchase #2	$168.51	13.736%	$191.6565	$191.66	$191.65	$191.70
Purchase #3	$19.38	8.807%	$21.0868	$21.09	$21.10	$21.10
Purchase #4	$89.33	12.211%	$100.2381	$100.24	$100.25	$100.20
Purchase #5	$189.61	12.682%	$213.6563	$213.66	$213.65	$213.70
Purchase #6	$131.35	4.565%	$137.3461	$137.35	$137.35	$137.30
Purchase #7	$133.96	7.494%	$143.999	$144.00	$144.00	$144.00
7 purchase totals =	$850.12		$939.3877	$939.40	$939.40	$939.40