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	$46.52	8.697%	$50.5658	$50.57	$50.55	$50.60
Purchase #2	$32.38	11.497%	$36.1027	$36.10	$36.10	$36.10
Purchase #3	$84.35	10.718%	$93.3906	$93.39	$93.40	$93.40
Purchase #4	$174.33	5.378%	$183.7055	$183.71	$183.70	$183.70
Purchase #5	$90.88	13.640%	$103.276	$103.28	$103.30	$103.30
Purchase #6	$82.61	9.468%	$90.4315	$90.43	$90.45	$90.40
Purchase #7	$199.79	8.314%	$216.4005	$216.40	$216.40	$216.40
7 purchase totals =	$710.86		$773.8726	$773.88	$773.90	$773.90