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	$131.52	7.219%	$141.0144	$141.01	$141.00	$141.00
Purchase #2	$190.53	13.645%	$216.5278	$216.53	$216.55	$216.50
Purchase #3	$156.27	9.288%	$170.7844	$170.78	$170.80	$170.80
Purchase #4	$40.34	7.430%	$43.3373	$43.34	$43.35	$43.30
Purchase #5	$190.39	13.855%	$216.7685	$216.77	$216.75	$216.80
Purchase #6	$29.48	6.135%	$31.2886	$31.29	$31.30	$31.30
Purchase #7	$75.59	3.297%	$78.0822	$78.08	$78.10	$78.10
7 purchase totals =	$814.12		$897.8032	$897.80	$897.85	$897.80